Water Source Alternative Options Assessment for the Metropolitan Supply

Rainwater Tanks Concept Report

Prepared for Watercare Services Ltd

Prepared by Beca Limited

9 December 2020

Creative people together transforming our world

| Rainwater use assessment |

Revision History Revision Prepared By Description Date Nº 1 Haddon Smith Frist draft 18 th Nov 2020

2 Haddon Smith Final draft 27 th Nov 2020

3 Haddon Smith Final 9th Dec 2020

Document Acceptance Action Name Signed Date Prepared by Haddon Smith 9th Dec 2020

Reviewed by Jon Reed 9th Dec 2020

Approved by Clive Rundle 9th Dec 2020

on behalf of Beca Limited

© Beca 2020 (unless Beca has expressly agreed otherwise with the Client in writing).

This report has been prepared by Beca on the specific instructions of our Client. It is solely for our Client’s use for the purpose for which it is intended in accordance with the agreed scope of work. Any use or reliance by any person contrary to the above, to which Beca has not given its prior written consent, is at that person's own risk.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | i

Contents

Executive Summary ...... 1 1 Introduction ...... 3 1.1 Background...... 3 1.2 This report ...... 4 1.3 Purpose of this report ...... 5 1.4 Scenarios modelled in the 2015 report ...... 6 1.5 Storage developed by rainwater tanks ...... 8 2 Tanker demand during dry periods ...... 10 3 Modelled yield of rainwater tanks at Watercare’s Peak Level of Service ...... 13 4 Modelled yield of rainwater tanks at Watercare’s Annual average drought Level of Service ...... 19 5 Advantages and disadvantages of rainwater tanks ...... 22 5.1 Potential benefits of rainwater tanks ...... 22 5.2 Disadvantages of rainwater tanks ...... 22 6 Yield recommendations ...... 24 7 Cost estimate ...... 26 7.1 Capital costs ...... 26 7.2 Operational costs ...... 26 7.3 Optimistic scenario costing ...... 28 8 Conclusions ...... 29

Appendices

Appendix A – Peak results tables Appendix B – Annual average yield plots for scenarios 1-4

Waikato River Water Take and Discharge Proposal – Board of Inquiry | ii

Tables

Table 1-1: Definition of tank sizes ...... 7 Table 4-1: Annual average drought yields obtained under the optimistic scenario for differnce use types ...... 20 Table 6-1: Summary of different use types ...... 24 Table 7-1: Capital costs of rain tank installations by tank size ...... 27 Table 7-2: Average capital costs by development type based on the optimistic scenario ...... 27 Table 7-3: Operational costs ...... 27 Table 7-5: Optimistic scenario cost analysis summary ...... 28 Table A1: 2019 rain tank peak results under outdoor use ...... 32 Table A2: 2020 rain tank peak results under outdoor use ...... 33 Table A3: 2019 rain tank peak results under non-potable use...... 34 Table A4: 2020 rain tank peak results non-potable use ...... 35 Table A5: 2019 rain tank peak results all use ...... 36 Table A6: 2020 rain tank peak results under all use ...... 37

Waikato River Water Take and Discharge Proposal – Board of Inquiry | iii

Figures

Figure 1-1: How this report feeds into the overall options assessment process in the “Water Source Options Assessment for the Metropolitan Supply” report ...... 6 Figure 1-2: Definition of the modelled scenarios in the 2015 report, note that the uptake dates shown here have been moved forward by five years for the purpose of this 2020 update (i.e. references to 2050 in the table are 2055 in results produced for this report)...... 7 Figure 1-3: Summary of rainwater tank penetration over a 35 year period (optimistic scenario) ...... 8 Figure 1-4: Simplified model schematic ...... 8 Figure 1-5: Total rain tank storage volume under the Optimistic uptake scenario, compared to Watercare's total lake storage volume and Watercare’s smallest storage lake (Hays Creek) ...... 9 Figure 2-1: Tanker consumption by financial year ...... 10 Figure 2-2: Normalised monthly tanker consumption for the 2016 to 2020 financial years ...... 11 Figure 2-3: Timeseries showing relationship between total tanker consumption and monthly rainfall . 11 Figure 2-4: Relationship between tanker consumption and monthly rainfall between February 2015 and June 2020 ...... 12 Figure 3-1: Average yield over peak 5 days in various recent dry years under the optimistic scenario (note that the 5 days averaged are the highest individual 5 days of demand, not the highest 5 consecutive days) ...... 14 Figure 3-2: Average yield in February in various recent dry years under the optimistic scenario ...... 14 Figure 3-3: Average yield in January, February and March in various recent dry years under the optimistic scenario ...... 15 Figure 3-4: Average volume and demand met by medium sized tanks at single residential properties during the 2020 summer ...... 16 Figure 3-5: Average volume and demand met by medium tanks at single residential properties during the 2014 summer ...... 17 Figure 3-6: Average yield over different peak periods under different tank sizes in 2019 and 2020 with rainwater tanks supplying non-potable use ...... 18 Figure 4-1: Optimistic scenario rainwater tank annual average drought yield at 2055 - 36% of properties by 2055 ...... 20 Figure 4-2: Average yield through the year from simulations corresponding to dry [99% series] median [50% series] and wet [1% series] years under the optimistic scenario supplying non-potable demand...... 21 Figure 6-1: Growth in the annual average drought yield of rainwater tanks under the ‘optimistic’ scenario ...... 25 Figure 7-1: Annual capital and operation costs of rainwater tanks over time (non-cumulative) ...... 28 Figure B1: Scenario 1 rainwater tank annual average yield at 2055 - 23% of properties by 2055 ...... 39 Figure B2: Scenario 2 rainwater tank annual average yield at 2055 - 31% of properties by 2055 ...... 39 Figure B3: Scenario 3 rainwater tank annual average yield at 2055 - 57% of properties by 2055 ...... 40 Figure B4: Scenario 4 rainwater tank annual average yield at 2055 - 66% of properties by 2055 ...... 40

Waikato River Water Take and Discharge Proposal – Board of Inquiry | iv

Abbreviations and Definitions

Abbreviations Definitions THAB Terrace Housing and Apartment Buildings m3/ day Cubic metres per day ML/d Mega litres per day AIC Annualised incremental cost

Waikato River Water Take and Discharge Proposal – Board of Inquiry | v

| Executive Summary |

Executive Summary

This report presents the potential for rainwater tanks to contribute as a strategic water resource for the Auckland region. It updates previous work completed by CH2M Beca, described in the 2015 report Impact of Rainwater Tanks on the Level of Service for Water Supply in Auckland. This 2020 update has been prepared to support Watercare’s updated application to abstract water from the Waikato River that was first lodged with the Waikato Regional Council in December 2013 and is now to be decided by a Board of Inquiry. It considers how rainwater tanks could impact the supply/demand balance by 2055 at Watercare’s two relevant Levels of Service (LoS):

1. Demand restrictions within the Metropolitan supply area are not required more frequently than 1 in 20 years (described in this report as the ‘ peak Level of Service’); and 2. Annual average demand within the Metropolitan supply area can be met in a drought with a 1% probability of occurrence leaving 15% residual capacity in its reservoirs (described in this report as the ‘ annual average drought Level of Service’). The analysis described in this report focuses on the optimistic scenario presented in the 2015 report. This scenario was designed to represent the maximum possible uptake of rainwater tanks that could realistically be achieved, assuming very strong legislative drive, subsidies and community desire. Under this scenario, installation of rainwater tanks at new properties is mandated from 2023 with 100% of new properties having tanks installed from 2035 onwards. Rainwater tanks are also retrofitted at existing properties at a rate of 3,000 properties per year from 2023 onwards. This results in 270,000 rainwater tanks being installed by 2055; coving approximately 36% of Auckland’s domestic properties.

The report concludes that, if approximately 270,000 small, medium and large rainwater tanks are installed to supply non-potable use within new and existing properties by 2055, the potential benefit is be expected to be:

● 15 ML/d at the peak Level of Service; and ● 30 ML/d at the annual average drought Level of Service. The reason that rainwater tanks can make a larger contribution to the annual average drought Level of Service is that, during dry summers, by the time peak demand day occurs many rainwater tanks will by empty due to the combination of low rainfall and high summer demand. However, even during a drought year they do provide some supply when rain occurs (particularly during the winter) which leads to the modelled yield on average across the year. A disadvantage of rainwater tanks compared to some of the other sources considered is that yields increase incrementally based on the staged installation of tanks, with only 3.8 ML/d of annual average drought yield expected to be achievable by 2030. Cost estimates for the optimistic scenario have been updated to 2020 prices, resulting in the following outputs 1:

● Annual capital costs for tank installations rise from $28 million in 2023 to $58 million in 2055 over the 32-year period, representing a total capital cost of $1623 million; ● Operating costs of rain tanks, excluding periodic replacement of the pumps and tanks, is $1.15 per cubic meter (calculated based on the average annual drought yield);

1 Note that the estimates are based on broad assumptions and high-level concepts only and considered accurate in the order -25% to +50%. They are suitable for option comparison purposes only and should not be used for budgeting purposes.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 1

| Executive Summary |

● The net present value cost of the optimistic scenario (capital and operational cost) is estimated as $726 million; and ● The annualised incremental cost (NPV of the scheme divided by the discounted annual average drought yield) is $15 [$/m 3] The main outputs of this report, as described above, are summarised in Table ES-1.

Table ES-1: Summary of rainwater tank yields and costs

Output Value Peak LoS yield 15 ML/d Annual average drought LoS yield 30 ML/d Total capital cost over 32-year installation period $1623 million Operating costs of rain tanks $1.15 [$/m 3] Net present value cost $726 million Annualised incremental cost $15 [$/m 3]

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 2

| Introduction |

1 Introduction

1.1 Background Watercare Services Limited (“ Watercare ”) is a lifeline utility providing water and wastewater services to a population of 1.67 million people in Auckland. Its services are vital for life, keep people safe and help communities to flourish. More specifically, Watercare is the council-controlled organisation of Auckland Council responsible for municipal water supply within Auckland, and the provider of bulk water supply services to Papakura in south Auckland and Pokeno and Tuakau in the Waikato District. 2

Watercare supplies approximately 440,000 cubic metres of water per day (“ m3/day ”) on average across the year, derived from a range of sources and treated to the Ministry of Health Drinking Water Standards for New Zealand 2005 (revised 2018).

Watercare’s three main metropolitan water supply sources are: 3

. Water storage lakes in the Hūnua and Waitākere ranges; . A groundwater aquifer in Onehunga; and . The Waikato River. The exact proportion supplied from each source varies daily, depending on a range of factors including the levels in the storage lakes, forecast rainfall, treatment plant capacity, and maintenance requirements. In December 2013, Watercare applied to the Waikato Regional Council (“ WRC ”) for resource consents to authorise abstracting an additional 200,000 m 3/day (net) of water from the Waikato River, a new water intake structure and discharges from a new water treatment plant. Since that time, Watercare’s water take application (and the associated applications) have been on hold while the WRC processes and determines other applications to take water from the Waikato River Catchment that were lodged before Watercare’s application. During the period from late 2019 through to mid-2020, the Auckland region experienced one of the most extreme drought events in modern times with rainfall for the period between January and May 2020 being approximately 30% of what would normally be expected for that period. At Watercare’s recommendation, in May 2020 Auckland Council imposed water use restrictions in Auckland for the first time since the early 1990s. Watercare also took additional steps to improve security of supply during the drought by exercising emergency powers under section 330 of the Resource Management Act 1991 (RMA ), 4 and by re-establishing supply from previously decommissioned sources. 5 While the above steps have been taken to make sure Auckland’s short term water supply requirements are met, the focus has now turned to the future. Watercare are now planning how demand can be met over the long term by securing sustainably sourced water to achieve:

. Certainty of supply in up to a 1:100-year drought with 15% residual dam storage; and

2 Under a bulk supply agreement with Waikato District.

3 Watercare also operates individual water supplies from various sources including groundwater and surface water for several other communities such as Muriwai, Algies Bay, Snells Beach, Bombay, Waiuku, Warkworth, Helensville and Wellsford.

4 Reduced environmental flows from the Waitakere, Wairoa and Cosseys Storage Lakes, and a short term take from the Waikato River. 5 Groundwater bores at Pukekohe and the Hays Creek Storage Lake in Papakura.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 3

| Introduction |

. Certainty of supply to meet peak demand. On 30 June 2020, after considering advice provided by the Environmental Protection Authority, the Minister for the Environment issued a direction under section 142(2) of the RMA to call in Watercare’s 2013 application and refer the matter to a Board of Inquiry to determine the application. The Minister’s direction recognised Watercare’s application as a proposal of national significance. Given the passage of time since the 2013 application was lodged, Watercare has updated the application to address a range of matters including updates to population and demand assessments, changes to the policy framework within which the application is to be considered, consultation that has taken place, reassessment of potential water supply sources and intake options, and updated assessments of environmental effects including the effect that granting Watercare’s application would have on the allocation available to other users. The updated application will be heard by the Board of Inquiry.

The most significant revision to the 2013 application, resulting directly from Watercare’s ongoing engagement with Waikato-Tainui is a reduction in the volume of the proposed water take from 200,000 m3/day (net) to 150,000 m3/day (net). This reduction reflects Waikato-Tainui’s special relationship with the Waikato River as outlined in the Waikato-Tainui Raupatu Claims (Waikato River) Settlement Act 2010. It recognises Waikato-Tainui’s relationship with the Waikato River and its respect for the River lies at the heart of Waikato-Tainui’s spiritual and physical wellbeing, tribal identity and culture.

Watercare currently holds three resource consents authorising the abstraction of water from the Waikato River adjacent to the Waikato Water Treatment Plant (“ Waikato WTP ”) near Tuakau as follows: a) Resource consent 960089.01.04 authorising a net take rate of up to 150,000 m 3/day (net) at any time of the year. b) Resource consent 141825.01.01 (referred to as the “Seasonal Water Take” consent) authorising a take rate of up to:

i) 100,000 m 3/day (net) during the period 1 May to 30 September (inclusive); and ii) 100,000 m 3/day (net) during the period 1 October to 30 April (inclusive) when the 7-day rolling average flow of the Waikato River at Rangiriri exceeds 330.03 m 3/second. c) Resource consent 142090.01.01 (referred to as the “Hamilton City Council Water Allocation” consent), authorising a net take rate of up to 25,000 m 3/day (or such lesser volume as determined by Hamilton City Council as being available for any given day) during the period 1 October to 30 April (inclusive). This is a short-term consent till 1 May 2023. In the event that the consent sought through the Board of Inquiry process is granted for the volume sought, Watercare proposes that its Seasonal Water Take consent and Hamilton City Council Water Allocation consent would be surrendered. Watercare’s combined take from the Waikato River under its existing resource consent 960089.01.04, and the new water take consent sought through the Board of Inquiry would not exceed a year round take volume of 300,000 m 3/day 9 (net).

1.2 This report

This report provides an assessment of the potential for local rainwater tanks to be considered as a strategic water source for Auckland, prepared to support the application to be considered by the Board of Inquiry. A ‘strategic’ water source has been defined by Watercare and Beca as a source capable of supplying more than 20 ML/d towards the annual average drought level of service. In 2015 Watercare Services Limited (Watercare) engaged CH2M Beca Ltd (CH2M Beca) to assess the potential water resources benefits of rainwater tanks. This culminated in CH2M Beca’s report Impact of Rainwater

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 4

| Introduction |

Tanks on the Level of Service for Water Supply in Auckland. This report considered how rainwater tanks could impact the supply/demand balance by 2050 at Watercare’s two relevant Levels of Service: 1. Demand restrictions within the Metropolitan supply area are not required more frequently than 1 in 20 years (described in this report as the ‘ peak Level of Service’); and 2. Annual average demand within the Metropolitan supply area can be met in a drought with a 1% probability of occurrence leaving 15% residual capacity in its reservoirs (described in this report as the ‘ annual average drought Level of Service’). A high-level cost assessment was carried out, to enable the costs and benefits of rainwater tanks to be compared with other future water resource schemes.

Since 2015, particularly in response to the 2019/2020 drought, the subject of rainwater tanks has been a prominent subject of public discussion. As a result, Watercare appointed Beca Ltd (Beca) to provide some updated information in related to rainwater tanks. This report should be read in conjunction with the original CH2M Beca (2015) report.

1.3 Purpose of this report The 2015 report was comprehensive and remains relevant to this options assessment process. This report is not a complete update of the 2015 report, but reviews and updates a number of aspects of it. The 2015 report should therefore be read in conjunction with this report to understand the methodology taken to assess the potential benefit of rainwater tanks. This report includes the following:

. Analysis of recent water tanker sales to gauge the performance of existing rainwater tanks throughout recent dry periods; . Revisiting the rainwater tank Peak Level of Service analysis, particularly with regard to the potential benefit that rainwater tanks could have made during the 2019 and 2020 dry summers; . Develop additional detailed information about the annual average drought yield of rainwater tanks during drought conditions; . Comparing the scale of total storage volumes that could realistically be obtained from rainwater tanks with Watercare’s existing dam storage; and . Update the cost estimate to 2020 prices.

This report forms an input to the wider options selection process. The general approach to this process is summarised as Figure 1-1. This shows a number of different technical reports being used to support the wider options assessment process. This rainwater tank report is one of these inputs. The options assessment process considers the positive and negative aspects of these potential water resources schemes to enable a preferred option to be recommended.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 5

| Introduction |

Figure 1-1: How this report feeds into the overall options assessment process in the “Water Source Options Assessment for the Metropolitan Supply” report

1.4 Scenarios modelled in the 2015 report

Five different scenarios were modelled in the 2015 report, as summarised in Figure 1-2. Each of these scenarios is split into three sub-scenarios according to the demand type that is met by the rainwater tanks ( outdoor , non-potable or all demand ). Scenarios 1 to 4 all model the potential yield that can be achieved using large tanks.

As neither the installation of large tanks at all properties or the uptake rates of scenarios 2-4 is expected to be practical, a fifth ‘optimistic’ scenario was developed using a mixture of tank sizes (shown in Table 1-1). This shows a mixture of tank sizes for different types of development, with a minimum size of 1,000L up to 50,000 L for houses on large lots. The rate of implementation included in scenario 5 is shown as Figure 1-3, extending over a 35 year period. This results in approximately 36% of Auckland’s domestic properties having rainwater tanks installed over a 35 year period. Figure 1-4 is a simplified schematic of the model developed for the 2015 report. Modelling is completed using ‘Monte Carlo’ methodology where the model is run hundreds of times using model inputs (such as occupancy and tank size) randomly generated from underlying probability distributions.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 6

| Introduction |

Figure 1-2: Definition of the modelled scenarios in the 2015 report, note that the uptake dates shown here have been moved forward by five years for the purpose of this 2020 update (i.e. references to 2050 in the table are 2055 in results produced for this report)

Table 1-1: Definition of tank sizes

Development Type Tank Size (Litres) Low Med High Large Lot 25,000 50,000¹ Single House 1,000 5,000 25,000 Mixed Housing 1,000 2,000 5,000 Terrace Housing and Apartment Buildings 25,000 50,000¹ (THAB)² Notes: 1. Where 50,000 L of rainwater tank is modelled (i.e. the High Scenario for THAB and Large Lot zones), It is assumed these will be made up of two 25,000 L tanks. 2. It is assumed that in the development with multiple households per parcel (e.g. the THAB zones), the tank volume will be shared equally between each household. The values in Appendix C3 can be used to convert the above values (assumed to be per parcel) to a tank volume per household, to be used in the GoldSim Model.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 7

| Introduction |

Figure 1-3: Summary of rainwater tank penetration over a 35 year period (optimistic scenario)

Figure 1-4: Simplified model schematic

1.5 Storage developed by rainwater tanks The total storage developed by a rainwater tank strategy depends on a combination of the penetration and size of the

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 8

| Introduction |

rainwater tanks that have been developed. The potential total storage developed by rainwater tanks for the ‘optimistic’ scenario is estimated as approximately 1.3 GL over a 30 year period. For comparison, Watercare’s total storage in 2020 is approximately 95 GL. Figure 1-5 shows the potential total volume of storage, compared with Watercare’s total lake storage in 2020 and its smallest lake (Hays Creek).

Figure 1-5: Total rain tank storage volume under the Optimistic uptake scenario, compared to Watercare's total lake storage volume and Watercare’s smallest storage lake (Hays Creek)

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 9

| Tanker demand during dry periods |

2 Tanker demand during dry periods

Tanker demand during dry periods provides a useful indicator of the extent to which rainwater tanks refill naturally and provide a material source of water for domestic use during those periods. Watercare sell potable water from the metropolitan and non-metropolitan networks to commercial tanker operators from eleven filling stations across Auckland, with three new filling stations soon to be operational. Volumes are recorded and the commercial operators are charged for the water on a volumetric basis.

Records of consumption by tanker operators are maintained by Watercare and are summarised in Figure 2-1 as total tanker consumption in each financial year (2016-2020).

There is a clear relationship between tanker sales and rainfall, with higher sales in dry periods. Figure 2-3 is a timeseries showing total monthly tanker sales between February 2015 and June 2020 compared to monthly rainfall. It shows that each year tanker sales increase in the summer months, with especially high sales throughout the 2019/2020 drought. Furthermore, looking at the minimum sales each year, we see that the underlying winter sales are typically less than 10,000m 3. The impact of dry weather on tanker sales is demonstrated further by Figure 2-4; a scatter plot of monthly rainfall vs total tanker sales. It shows a clear trend, with high tanker sales in months of low rainfall. With one exception, all months with sales greater than 40,000m 3 occur between December and March

These results show that customers who use rain tanks require little water from Watercare during the winter months but may require top ups during ordinary summers. However, during drought conditions the ability of rainwater tanks to meet demand is reduced and therefore customers with rainwater tanks often rely on Watercare’s supply. The implication of these results in terms of the supply / demand balance is that rainwater tanks may be suitable to contribute to the annual average drought supply / demand balance, however they are likely to be limited in ability to contribute to the peak supply / demand balance. This is because during drought conditions, by the time peak day demand occurs it is likely that many of the rainwater tanks will be empty.

Figure 2-1: Tanker consumption by financial year

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 10

| Tanker demand during dry periods |

Figure 2-2: Normalised monthly tanker consumption for the 2016 to 2020 financial years

Figure 2-3: Timeseries showing relationship between total tanker consumption and monthly rainfall

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 11

| Tanker demand during dry periods |

Figure 2-4: Relationship between tanker consumption and monthly rainfall between February 2015 and June 2020

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 12

| Modelled yield of rainwater tanks at Watercare’s Peak Level of Service |

3 Modelled yield of rainwater tanks at Watercare’s Peak Level of Service

Watercare’s peak level of service is to meet peak day demand during a dry summer, without imposing restrictions more frequently than 1 in 20 years. The yield available from Watercare’s water sources at the peak level of service is generally constrained by the capacity of the water treatment plants and water transmission infrastructure, rather than a hydrological constraint.

Daily demand and how it varies during a hot, dry summer is the main driver for the peak Level of Service. To determine the potential of rainwater tanks to contribute to peak supply requirements, four recent dry summers (2013, 2014, 2019 and 2020) were modelled that approximately represent demand at the peak Level of Service. These scenarios enable the potential benefit of rainwater tanks at the peak Level of Service to be assessed. Results from Beca’s modelling show that the ability of rain tanks to contribute to peak demand varies considerably depending on which peak period is considered. This is demonstrated by Figure 3-1, Figure 3-2 and Figure 3-3, which give average yield under the optimistic scenario for the following:

. The peak 5 days; . The February period; and . The 3-month summer period respectively. Yield obtained in the peak five days of each year is highly variable, even during dry summers periods. This is demonstrated by Figure 3-1, which shows that non-potable yield over the peak five days ranges from as little as 5 ML/d in 2020 to 32.5 ML/d in the 2014 summer. It also shows the difference between the different water uses; where rainwater tanks have been used for all demand, the peak period yield is often lower as the tanks can be empty after a dry spring. This observation suggests that, if peak day supply is targeted, the potential best use for rainwater tanks is to use the water to meet non-potable demand.

Over the February period (on average) the yield of the rainwater tanks shows an improved performance compared to the peak day analysis (Figure 3-2). Average yield over the four years reviewed is between approximately 15 and 25 ML/d for the non-potable scenario. There is also less variation between the use type in results for average February yield when compared to peak 5 days yield. There are two factors that explain this: Firstly, in very dry periods all available water is used regardless of the use type, so total yield is essentially equal to total water available, which is similar for all three use types. Secondly, while tanks at terrace/apartment and mixed housing properties tend to empty during dry periods, tanks at large lot properties do not; thus, a small base demand throughout February is met regardless of the rainfall.

Figure 3-3 presents the same data but for the whole summer period (January, February and March). This shows comparable yields to February would be expected over the whole summer.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 13

| Modelled yield of rainwater tanks at Watercare’s Peak Level of Service |

Figure 3-1: Average yield over peak 5 days in various recent dry years under the optimistic scenario (note that the 5 days averaged are the highest individual 5 days of demand, not the highest 5 consecutive days)

Figure 3-2: Average yield in February in various recent dry years under the optimistic scenario

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 14

| Modelled yield of rainwater tanks at Watercare’s Peak Level of Service |

Figure 3-3: Average yield in January, February and March in various recent dry years under the optimistic scenario

To serve as an example of the behaviour of rainwater tanks throughout the duration of a dry summer, the performance of medium sized tanks at single residential properties under all demand and non- potable use in 2020 and 2014 is shown as Figure 3-4 and Figure 3-5 respectively. Looking at the 2020 result, we see that under both use types average tank volumes at mid-December are approximately 5000 L. However, with all demand being supplied average volumes quickly reduces to low levels by the start of January. Because of this, both demand and tank volumes remain low/zero for most of January and February. In contrast, under non-potable use, average tank volumes never reach zero and some demand is still met throughout the period, although at limited rates. Inspection of the 2014 result in Figure 3-5, similar behaviour is observed, with tank volumes quickly reducing under all demand ; however more demand is met due to small amounts of rainfall occurring throughout the summer.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 15

| Modelled yield of rainwater tanks at Watercare’s Peak Level of Service |

Figure 3-4: Average volume and demand met by medium sized tanks at single residential properties during the 2020 summer

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 16

| Modelled yield of rainwater tanks at Watercare’s Peak Level of Service |

Figure 3-5: Average volume and demand met by medium tanks at single residential properties during the 2014 summer

Another important factor that influences rainwater tank yields during peak periods is the size of the tanks installed. This is made evident by Figure 3-6, which gives the average yield in 2019 and 2020 for non-potable use under the three different peak periods for large, medium and small tanks. It shows that during peak periods large tanks supply considerably more water than medium and small tanks. The effect is particularly pronounced in the peak 5 days, where medium and small tanks provide almost no water as most of them are empty.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 17

| Modelled yield of rainwater tanks at Watercare’s Peak Level of Service |

Figure 3-6: Average yield over different peak periods under different tank sizes in 2019 and 2020 with rainwater tanks supplying non-potable use

To summarise, the important findings of Beca’s analysis with regard to the supply demand balance are as follows:

● Rainwater tanks are limited in their ability to contribute to peak day demand, as during dry periods most tanks are likely to be empty on the peak days of the year; ● Rainwater tank yield on the peak days of the year is highest for Outdoor use, followed by non- potable use and lowest for all demand; ● Rainwater tank yield during the peak month of February or the entire peak summer period of January, February and March is more reliable than the peak day yield (due to the benefit of small rainwater events); and ● The size of the rainwater tanks installed is very influential to yields within peak periods. If Watercare wish to use rainwater tanks to contribute to peak demand, the installation of large tanks should be encouraged.

The tables in Appendix A give additional details for the 2019 and 2020 summers, broken down for each of the tank sizes and each of the development types.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 18

| Modelled yield of rainwater tanks at Watercare’s Annual average drought Level of Service |

4 Modelled yield of rainwater tanks at Watercare’s Annual average drought Level of Service

Watercare’s drought Level of Service relates to meeting annual average demand during a drought of a certain severity. It is controlled by the yield of the water sources at these extremes. Three potential Levels of Service have been assessed, based on failure of the water resources in 1 in 50, 1 in 100 and 1 in 200 year drought events.

CH2M Beca’s 2015 report gave results for yield as percentiles (strictly percent exceedance) of daily yield calculated based on a synthesized 1000-year rainfall time series. Results presented in this report take an alternative approach, where percentiles are calculated based on the average annual drought yield of each financial year in the 1000-year time series. Output gives the yields that could be achieved by 2055, under the assumptions of the optimistic scenario .

Table 4-1 shows percentage exceedance for the optimistic scenario for each use type against the three drought levels of service and also a “typical” 50% exceedance year, with Figure 1-2 giving the same output as a plot.

There are a number of important aspects of these results to note:

● Results for the annual average drought yield percentiles have a flatter profile when compared to those given in Rainwater Tanks on the Level of Service for Water Supply in Auckland for daily yield percentiles. This shows that while rainwater tank yield varies considerably throughout the year and day to day, depending on the amount of rainwater in the preceding days and weeks, annual average drought yield is more predictable. ● The annual average drought yield in the Optimistic scenario, designed to represent the maximum possible yield that could realistically be achieved during a 1-100 year drought, results in yields of 50.8ML/d, 29.5 ML/d and 11.9ML/d if rainwater tanks are used to supply all use, non-potable demand and outdoor only demand respectively. ● The reliability of rainwater tank yield throughout the year is demonstrated by Figure 4-2. It gives the average daily yield for the optimistic scenario from simulations corresponding to dry [99% series], median [50% series] and wet [1% series] years in the 1000-year synthetic time series. It shows that rainwater tank yield varies considerably between wet, median and dry years during the summer months; however, is essentially constant between June and November. This behaviour indicates that, while rainwater tanks are limited in their ability to contributed to peak demand in dry years, they have the potential to contribute to annual average drought yield by conjunctive use (i.e. using the rainwater tanks throughout the winter, instead of the supply lakes, to let the supply lakes refill).

Similar plots to Figure 4-1 but for Scenarios 1-4 are given in Appendix B.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 19

| Modelled yield of rainwater tanks at Watercare’s Annual average drought Level of Service |

Table 4-1: Annual average drought yields obtained under the optimistic scenario for differnce use types

Percent Equivalent level Outdoor use Non-potable All use [ML/d] exceedance of service [ML/d] [ML/d] 99.5% 1-200 year 11.7 29.2 49.6 99% 1-100 year 11.9 29.7 50.8 98% 1-50 year 12.1 30.1 53.0 50% - 12.8 33.5 64.2

Figure 4-1: Optimistic scenario rainwater tank annual average drought yield at 2055 - 36% of properties by 2055

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 20

| Modelled yield of rainwater tanks at Watercare’s Annual average drought Level of Service |

Figure 4-2: Average yield through the year from simulations corresponding to dry [99% series] median [50% series] and wet [1% series] years under the optimistic scenario supplying non-potable demand.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 21

| Advantages and disadvantages of rainwater tanks |

5 Advantages and disadvantages of rainwater tanks

5.1 Potential benefits of rainwater tanks Rainwater tanks can provide householders with a variety of benefits and opinions are divided about their usefulness. This study reviews the benefits of rainwater tanks solely from the position of water resources at Watercare’s Level of Service – i.e. during a drought or a very dry period. It does not attempt to quantify or address these other benefits; however, some of the more significant potential benefits and disadvantages are discussed here.

Other benefits of rain tanks potentially include:

● Stormwater attenuation (although for this to work they cannot by full); ● Storage to provide a resilience benefit; ● A lifestyle benefit – people feel ‘good’ about using rainwater in their daily lives as they feel as if they are ‘making a difference’; and ● Employment through the creation of jobs to install and maintain the rainwater tanks and treatment systems.

5.2 Disadvantages of rainwater tanks When compared to other source options, rainwater tanks for water supply have a number of unique disadvantages. Many of these are the result of the highly distributed nature of rainwater tanks, as described here:

● Safety risks Rainwater tanks can pose a safety risk to households. This is due to the difficulty in providing and maintaining effective treatment processes at individual properties. The risk is highest for properties using rainwater tank water for drinking water; however, even if rainwater tanks are intended only for non-potable or outdoor use, there is still a risk that customers may inadvertently drink untreated rainwater. The installation of rainwater tanks can also increase back-flow risk.

● Increased peaking factor The results presented earlier in this report show that rainwater tanks can make a larger contribution to annual average demand than to peak demand due to higher yields over the winter months. This can decrease the cost effectiveness of the water supply system, as less of the infrastructure required on the peak days of the year is utilised throughout the remainder of the year.

● Maintenance In order to guarantee reliable yields in drought years rainwater tanks need to be regularly maintained. Regular maintenance is required to remove slit, check and maintain the pumps and clean the tanks. If rainwater is to be used for drinking water, maintenance of treatment systems and replacement of treatment chemicals need to be completed. To ensure that rainwater tanks are regularly maintained and yields available when required, Watercare would need guaranteed oversight of the tanks by some means.

● Social equity

The installation of rainwater tanks requires a large initial capital outlay, but then saves the household money by lower water bills. Results presented in this report suggest that the infrastructure requirements at peak, funded through water bills, will not reduce significantly if rainwater tanks

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 22

| Advantages and disadvantages of rainwater tanks |

are used as a water source. This means that residents with financial capacity to install rainwater tanks may inadvertently reduce their contribution to the infrastructure they rely on in peak periods, with that burden falling on poorer households.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 23

| Yield recommendations |

6 Yield recommendations

Table 6-1 summarises the Optimistic scenario yields and provides some high-level commentary on the cost and safety risks posed by each use type. Cells are coloured so the use type with the best characteristics in each category is green, with second and third use types in yellow and orange respectively. Table 6-1: Summary of different use types

● Peak LoS yield Annual average Safety risk Cost [ML/d] drought LoS yield [ML/d] Outdoor use Between 7 and 34 11.9 Lowest safety risk. Lowest cost. ML/d in the four No possibility of Pipe work is summer periods back flow events. independent of modelled house plumbing. Non-potable Between 5 and 33 29.7 Moderate safety Medium cost. use ML/d in the four risk. Backflow Plumbing needs summer periods events can occur. to be tied into the modelled Risks of cross- internal house connections. system, including backflow prevention devices All demand Between 1 and 26 50.8 Highest safety risk Highest cost. ML/d in the four Customers rely on Treatment system summer periods their own required, modelled treatment system plumbing into for drinking water house required treatment. including backflow Backflow events prevention could occur. devices.

Based on the information given in Table 6-1, Beca recommends that if a rainwater strategy is pursued, then it would be best to target non-potable use . This gives the best balance of maximising both peak and annual average drought yields at Watercare’s Levels of Service, while minimising installation costs and safety risks.

In terms of the yields that should be assumed for planning and option comparison purposes, we recommend the following:

● The estimate of the maximum peak day yield that could be achieved using rain tanks by 2055 (optimistic scenario assuming non-potable use) is 15 ML/d for Watercare’s 1 in 20 year peak day level of service ; and ● The estimate of the maximum annual average drought yield that could achieved using rainwater tanks by 2055 is 30ML/d (assuming non-potable use and the optimistic scenario ). It should be noted that there is some uncertainty about the peak yield due to the nature of different droughts, with non-potable peak yield under the optimistic scenario ranging between 5ML/d and 33ML/d in the four summer periods modelled. There is a risk that the peak day yield could be lower than 15 ML/d and if this option is taken forward the potential difference in yield should be included in headroom.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 24

| Yield recommendations |

Another disadvantage of rainwater tanks compared to other sources options is that yields increase incrementally based on the staged installation of tanks. The increasing yield over time is shown as Figure 6-1. It shows that, even under the generous uptake assumptions used in Optimistic Scenario, annual average drought yield is only 3.8 ML/d by 2030.

Figure 6-1: Growth in the annual average drought yield of rainwater tanks under the ‘optimistic’ scenario

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 25

| Cost Estimate |

7 Cost estimate

7.1 Capital costs The cost analysis detailed in CH2M Beca’s 2015 report has been updated to 2020 rates. The updated installation costs are provided in Table 7-1. The capital costs in Table 7-1 were used to develop capital costs for each development type, as given in

Table 7-2, taking into account the tank sizes expected to be installed at different development types (as per Table 1-1), and adjusted for new builds and alternative water uses.

Developments have a single tank per dwelling, with the exception of the terraced and apartment developments where all the dwellings within a parcel would share the same tank and pump. Therefore, these costs have been divided by the average number of households per parcel.

In line with Auckland Council’s removal of building consent costs for most rain tank installations, potential consenting costs have not been included. The capital cost for rainwater tanks in new builds has been reduced to reflect the lower installation costs in these properties. As costs could not be determined accurately, the connections to the roof and the labour costs have not been included. Where the water is used for outdoor use the plumbing labour costs have been removed. Based on these assumptions, Beca considers the cost estimate to be conservative (i.e. more likely to underestimate the total costs).

7.2 Operational costs Operational costs of rainwater tanks include pumping costs and maintenance costs such as cleaning. The pumping cost will be determined by a wide variety of factors including:

● Daily profile of water use; ● Water demand; and ● Water lift/pressure requirements.

Rather than attempting to make assumptions for each development type and water use, a single annual pumping cost has been calculated for all installations. The pumping cost assumptions for rainwater tanks are detailed in Table 7-3. The unit electricity cost of 0.15 $/kWh is the same as that used in Beca’s 2020 operational cost analysis of Waikato A. Given that (2020) domestic retail electricity prices in Auckland often exceed 0.22-0.23 $/kWh (and can be up to 0.295 $/kWh), this is cost is considered conservative. It is assumed that the pump will be running for 30min a day which is based on a daily household demand of 150 L/day and a flow rate of 5 L/min. The maintenance costs for a rainwater tank in the literature vary greatly depending on the source. Day to day maintenance is likely to be very low and a number of sources refer to a value of $25/annum. On top of this an allowance should be made for pump and tank replacement at the end of their life, however, renewal costs have been excluded in line with the cost estimates for other source options considered as part of the wider options assessment process.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 26

| Cost Estimate |

Table 7-1: Capital costs of rain tank installations by tank size

Tank Size (l) 1000 2000 5000 25,000 50,000 Tank Cost and delivery and $ 1,900 $ 2,500 $ 3,795 $ 8,050 $ 10,500 sand base Pump and base $ 1,300 $ 1,300 $ 1,300 $ 1,300 $ 1,300 Connection to roof and $ 1,000 $ 1,000 $ 1,000 $ 1,000 $ 1,000 collection system Inlet, outlet valve and $ 800 $ 800 $ 800 $ 800 $ 800 connections Plumbing Labour $ 2,500 $ 2,500 $ 2,500 $ 2,500 $ 2,500 Electrical Labour $ 1,100 $ 1,100 $ 1,100 $ 1,100 $ 1,100 Total capital cost (ex $ 8,600 $ 9,200 $ $ 14,750 $ 17,200 GST) 10,495

Table 7-2: Average capital costs by development type based on the optimistic scenario

Development type Large Lot Single Terrace Mixed Housing and Apartment Buildings (THAB) Tank Cost and delivery and sand base $ 9,683 $ 4,582 $ 828 $ 2,732 Pump and base $ 1,300 $ 1,300 $ 111 $ 1,300 Connection to roof and collection $ 1,000 $ 1,000 $ 85 $ 1,000 system Inlet, outlet valve and connections $ 800 $ 800 $ 800 $ 800 Plumbing Labour $ 2,500 $ 2,500 $ 2,500 $ 2,500 Electrical Labour $ 1,100 $ 1,100 $ 94 $ 1,100 Total capital cost (ex GST) Outdoor use (no New $ 10,917 $ 6,682 $ 1,697 $ 4,832 plumbing) Retrofit $ 13,883 $ 8,782 $ 1,783 $ 6,932 Pump supply New $ 11,783 $ 6,682 $ 1,809 $ 4,832 (Non potable and All Retrofit $ 16,383 $ 11,282 $ 4,488 $ 9,432 demand)

Table 7-3: Operational costs

Pump size 0.75 kW Hours operating/day 0.5 hours Electricity use/annum 136.875 kWh Unit cost of electricity 0.15 $/kWh Pumping cost/annum $21 Cost/annum Cleaning and maintenance $25 Cost/annum Total operating cost per tank $46 Cost/annum

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 27

| Cost Estimate |

7.3 Optimistic scenario costing

Using the capital and operational costs detailed in section 7.1, an NPV analysis of the optimistic scenario was completed to 2055. A summary of the outputs of this analysis are given as Table 7-46. Total capital and operation costs (non-cumulative) of the optimistic scenario in each year are given as Figure 7-1. Table 7-4: Optimistic scenario cost analysis summary

Total Capex $ Millions $1,623 2055 annual opex $12.6 NPV (5%) $726 AIC [$/m 3] $15

Figure 7-1: Annual capital and operation costs of rainwater tanks over time (non-cumulative)

6 Note that the estimates are based on broad assumptions and high-level concepts only and considered accurate in the order -25% to +50%. They are suitable for option comparison purposes only and should not be used for budgeting purposes. Tank and pump renewals are excluded.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 28

| Cost Estimate |

8 Conclusions

This report reviews the potential for rainwater tanks to contribute to Auckland’s water resources as a strategic source. It has reviewed the previous work carried out in 2015 and identifies the potential contribution at Watercare’s two Levels of Service. Five scenarios were considered in the 2015 report; from these the fifth scenario (‘optimistic’) with a combination of rainwater tanks for new properties and retrofitted to existing properties was adopted for this update. This scenario was designed to represent the maximum possible uptake of rain tanks that could realistically be achieved, assuming very strong legislative drive, subsidies and community desire. Under this scenario, installation of rainwater tanks at new properties is mandated from 2023 with 100% of new properties having tanks installed from 2035 onwards. Rainwater tanks are also retrofitted at existing properties at a rate of 3,000 properties per year from 2023 onwards. This results in 270,000 rainwater tanks being installed by 2055; 36% of Auckland’s domestic properties. Should this option be pursued, the considerable uncertainties in this assumed uptake, and other modelling assumptions, should be reviewed in further detail.

Review of the performance suggests that the best combination of yield at both ‘ peak ’ and ‘annual average drought’ demand is when the water is used for a combination of non-potable uses. This is the basis of our assessment, that the expected yield at the two Levels of Service are:

● 30 ML/d at annual average by 2055; and ● 15 ML/d at peak by 2055. However, a disadvantage of rainwater tanks compared to other sources options is that yields increase incrementally based on the staged installation of tanks, with only 3.8 ML/d of annual average drought yield expected to be achievable by 2030. The increasing yield over time is shown as Figure 6-1. There is some uncertainty about the peak yield due to the nature of different droughts. There is a risk that the peak day yield could be lower than 15 ML/d and if this option is taken forward the potential difference in yield should be included in headroom. In section 1.5 of this report we compare the total volume of storage from rainwater tanks with Watercare’s dam storage. We note that the total storage in this rainwater tank scenario is similar to Hays Creek dam, which Watercare is currently in the process of re-introducing to service. For comparison, the expected yield of this source is expected to be 6 ML/d (annual average drought) and 11.1 ML/d at peak (following completion of the planned WTP upgrade).

Cost estimates for the optimistic scenario have been updated to 2020 prices, resulting in the following outputs 1: ● Annual capital costs for tank installations rise from $28 million in 2023 to $58 million in 2055 over the 32-year period, representing a total capital cost of $1623 million; ● Operating costs of rain tanks, excluding periodic replacement of the pumps and tanks, is $1.15 per cubic meter (calculated based on the average annual drought yield); ● The net present value cost of the optimistic scenario (capital and operational cost) is estimated as $726 million; and ● The annualised incremental cost (NPV of the scheme divided by the discounted annual average drought yield) is $15 [$/m 3]

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 29

| Appendix A |

Appendix A – Peak results tables

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 30

| Appendix A |

Appendix A Peak results tables

The tables in Appendix A gives for the 2019 and 2020 summers the proportion of rainwater tanks that would be expected to supply water:

● Across the whole of the summer (January February and March); and ● On the five peak days that were observed during those summer periods. ● Yield figures given for the whole summer and each of the peak days and are based on the optimistic scenario uptake by 2055. The information is broken down for each of the tank sizes and each of the development types. This shows the detail behind the summary graphs (shown in Figure 3-1 to Figure 3-6) and enables the reader to understand the difference in rainwater tank performance under different conditions. This clearly shows how the tank size effects rainwater tank performance; larger tanks being able to support more demand, even over drier periods.

An interesting element of the peak 5 days results in each table is the lack of any trend between the water supplied and the rank of the peak day, i.e. water supplied on the actual peak day is often higher than that of the fifth highest peak day. This is because rainwater tank yield is constrained exclusively by rainfall, with all demand being met if water is available in the tanks.

Similar tables for the 2013 and 2014 summers are given in CH2M Beca’s 2015 report.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 31

| Appendix A |

Table A1: 2019 rain tank peak results under outdoor use 2019 Summer % of Average Date of peak and order of peak day (1 to 5) summer summer 1 2 3 4 5 outdoor outdoor 29/01/2019 19/02/2019 13/02/2019 30/01/2019 14/02/2019 demand demand supplied supplied (ML/d) Tank size Development type % ML/d % ML/d % ML/d % ML/d % ML/d Small Large Lot 100% 0.4 100% 0.6 100% 0.6 100% 0.6 100% 0.6 100% 0.6 Single House 41% 1.5 13% 0.7 52% 2.9 0% 0.0 6% 0.3 0% 0.0 Terrace Housing & Apartment Buildings 72% 4.4 84% 7.6 42% 3.7 17% 1.5 84% 7.5 17% 1.5 Mixed Housing 36% 2.2 6% 0.5 33% 3.0 0% 0.0 6% 0.5 0% 0.0 Mixed Suburban 36% 6.6 6% 1.6 33% 9.1 0% 0.0 6% 1.6 0% 0.0 Medium Large Lot 100% 0.4 100% 0.6 100% 0.6 100% 0.6 100% 0.6 100% 0.6 Single House 88% 3.3 100% 5.6 58% 3.3 57% 3.2 100% 5.6 57% 3.1 Terrace Housing & Apartment Buildings 72% 4.4 84% 7.6 42% 3.7 17% 1.5 84% 7.5 17% 1.5 Mixed Housing 56% 3.4 49% 4.5 33% 3.0 6% 0.5 49% 4.4 6% 0.5 Mixed Suburban 56% 10.3 49% 13.4 33% 9.1 6% 1.6 49% 13.2 6% 1.6 Large Large Lot 100% 0.4 100% 0.6 100% 0.6 100% 0.6 100% 0.6 100% 0.6 Single House 100% 3.8 100% 5.6 100% 5.6 100% 5.6 100% 5.6 100% 5.5 Terrace Housing & Apartment Buildings 88% 5.4 100% 9.0 66% 5.9 69% 6.2 100% 8.9 56% 4.9 Mixed Housing 77% 4.7 85% 7.7 42% 3.8 49% 4.4 85% 7.6 49% 4.4 Mixed Suburban 77% 14.2 85% 23.2 42% 11.5 49% 13.3 85% 22.9 49% 13.2

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 32

| Appendix A |

Table A2: 2020 rain tank peak results under outdoor use 2020 Summer % of Average Date of peak and order of peak day (1 to 5) summer summer 1 2 3 4 5 outdoor outdoor 19/02/2020 18/02/2020 20/02/2020 4/02/2020 11/02/2020 demand demand Development supplied supplied Tank size type (ML/d) % ML/d % ML/d % ML/d % ML/d % ML/d Small Large Lot 98% 0.5 94% 0.6 94% 0.6 94% 0.6 100% 0.6 100% 0.6 Single House 35% 1.6 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Terrace Housing & Apartment Buildings 47% 3.5 0% 0.0 0% 0.0 0% 0.0 17% 1.7 17% 1.7 Mixed Housing 28% 2.1 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Suburban 28% 6.3 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Medium Large Lot 98% 0.5 94% 0.6 94% 0.6 94% 0.6 100% 0.6 100% 0.6 Single House 68% 3.1 6% 0.4 6% 0.4 6% 0.3 31% 2.0 31% 1.9 Terrace Housing & Apartment Buildings 47% 3.5 0% 0.0 0% 0.0 0% 0.0 17% 1.7 17% 1.7 Mixed Housing 37% 2.7 0% 0.0 0% 0.0 0% 0.0 6% 0.6 6% 0.6 Mixed Suburban 37% 8.2 0% 0.0 0% 0.0 0% 0.0 6% 1.8 6% 1.8 Large Large Lot 100% 0.5 100% 0.7 100% 0.6 100% 0.6 100% 0.6 100% 0.6 Single House 98% 4.5 100% 6.6 100% 6.3 97% 6.0 100% 6.2 100% 6.2 Terrace Housing & Apartment Buildings 61% 4.5 17% 1.8 17% 1.7 17% 1.7 56% 5.5 17% 1.7 Mixed Housing 51% 3.8 6% 0.6 6% 0.6 6% 0.6 24% 2.4 24% 2.4 Mixed Suburban 51% 11.3 6% 1.9 6% 1.8 6% 1.8 24% 7.2 24% 7.1

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 33

| Appendix A |

Table A3: 2019 rain tank peak results under non-potable use 2019 Summer % of Average Date of peak and order of peak day (1 to 5) summer summer 1 2 3 4 5 non- non- 29/01/2019 19/02/2019 13/02/2019 30/01/2019 14/02/2019 potable potable demand demand supplied supplied Tank size Development type (ML/d) % ML/d % ML/d % ML/d % ML/d % ML/d Small Large Lot 98% 0.6 100% 0.8 95% 0.8 100% 0.8 100% 0.8 98% 0.8 Single House 26% 1.7 6% 0.5 37% 3.0 0% 0.0 3% 0.3 0% 0.0 Terrace Housing & Apartment Buildings 51% 5.3 56% 7.5 25% 3.3 0% 0.0 21% 2.8 0% 0.0 Mixed Housing 22% 2.3 6% 0.8 23% 3.0 0% 0.0 1% 0.1 0% 0.0 Mixed Suburban 22% 7.0 6% 2.4 23% 9.1 0% 0.0 1% 0.3 0% 0.0 Medium Large Lot 98% 0.6 100% 0.8 95% 0.8 100% 0.8 100% 0.8 98% 0.8 Single House 70% 4.5 83% 6.9 37% 3.0 31% 2.6 57% 4.7 31% 2.6 Terrace Housing & Apartment Buildings 51% 5.3 56% 7.5 25% 3.3 0% 0.0 21% 2.8 0% 0.0 Mixed Housing 36% 3.8 18% 2.4 23% 3.0 0% 0.0 6% 0.8 0% 0.0 Mixed Suburban 36% 11.4 18% 7.1 23% 9.1 0% 0.0 6% 2.4 0% 0.0 Large Large Lot 100% 0.7 100% 0.8 100% 0.8 100% 0.8 100% 0.8 100% 0.8 Single House 98% 6.3 100% 8.3 93% 7.7 100% 8.3 100% 8.3 100% 8.2 Terrace Housing & Apartment Buildings 64% 6.6 56% 7.5 34% 4.5 17% 2.2 56% 7.4 17% 2.2 Mixed Housing 54% 5.7 49% 6.6 24% 3.3 24% 3.2 49% 6.5 24% 3.2 Mixed Suburban 54% 17.0 49% 19.8 24% 9.9 24% 9.6 49% 19.7 24% 9.5

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 34

| Appendix A |

Table A4: 2020 rain tank peak results non-potable use 2020 Summer % of Average Date of peak and order of peak day (1 to 5) summer summer 1 2 3 4 5 non- non- 19/02/2020 18/02/2020 20/02/2020 4/02/2020 11/02/2020 potable potable demand demand supplied supplied Tank size Development type (ML/d) % ML/d % ML/d % ML/d % ML/d % ML/d Small Large Lot 86% 0.6 78% 0.7 78% 0.7 78% 0.7 88% 0.8 78% 0.7 Single House 25% 1.8 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Terrace Housing & Apartment Buildings 29% 3.4 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Housing 19% 2.2 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Suburban 19% 6.8 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Medium Large Lot 86% 0.6 78% 0.7 78% 0.7 78% 0.7 88% 0.8 78% 0.7 Single House 45% 3.3 6% 0.5 6% 0.5 6% 0.5 6% 0.5 6% 0.5 Terrace Housing & Apartment Buildings 29% 3.4 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Housing 23% 2.7 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Suburban 23% 8.1 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Large Large Lot 97% 0.7 94% 0.9 94% 0.9 94% 0.9 100% 0.9 94% 0.8 Single House 84% 6.1 83% 7.7 83% 7.5 83% 7.4 83% 7.4 83% 7.4 Terrace Housing & Apartment Buildings 35% 4.1 0% 0.0 0% 0.0 0% 0.0 17% 2.4 17% 2.4 Mixed Housing 30% 3.5 6% 0.9 6% 0.9 6% 0.9 6% 0.9 6% 0.9 Mixed Suburban 30% 10.4 6% 2.7 6% 2.6 6% 2.6 6% 2.6 6% 2.6

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 35

| Appendix A |

Table A5: 2019 rain tank peak results all use 2019 Summer % of Average Date of peak and order of peak day (1 to 5) summer summer 1 2 3 4 5 all use all use 29/01/2019 19/02/2019 13/02/2019 30/01/2019 14/02/2019 demand demand supplied supplied (ML/d) Tank size Development type % ML/d % ML/d % ML/d % ML/d % ML/d Small Large Lot 67% 1.1 78% 1.4 41% 0.7 49% 0.9 78% 1.4 49% 0.9 Single House 12% 1.9 0% 0.0 17% 3.0 0% 0.0 0% 0.0 0% 0.0 Terrace Housing & Apartment Buildings 21% 5.3 0% 0.0 12% 3.3 0% 0.0 0% 0.0 0% 0.0 Mixed Housing 9% 2.4 0% 0.0 11% 3.0 0% 0.0 0% 0.0 0% 0.0 Mixed Suburban 9% 7.3 0% 0.0 11% 9.1 0% 0.0 0% 0.0 0% 0.0 Medium Large Lot 67% 1.1 78% 1.4 41% 0.7 49% 0.9 78% 1.4 49% 0.9 Single House 32% 5.1 6% 1.0 17% 3.0 0% 0.0 6% 1.0 0% 0.0 Terrace Housing & Apartment Buildings 21% 5.3 0% 0.0 12% 3.3 0% 0.0 0% 0.0 0% 0.0 Mixed Housing 15% 3.7 0% 0.0 11% 3.0 0% 0.0 0% 0.0 0% 0.0 Mixed Suburban 15% 11.3 0% 0.0 11% 9.1 0% 0.0 0% 0.0 0% 0.0 Large Large Lot 73% 1.2 88% 1.6 56% 1.0 49% 0.9 78% 1.4 49% 0.9 Single House 65% 10.3 83% 14.8 40% 7.1 57% 10.1 83% 14.7 57% 10.0 Terrace Housing & Apartment Buildings 26% 6.7 17% 4.8 12% 3.3 0% 0.0 17% 4.8 0% 0.0 Mixed Housing 22% 5.6 6% 1.7 11% 3.0 0% 0.0 6% 1.7 0% 0.0 Mixed Suburban 22% 16.8 6% 5.2 11% 9.1 0% 0.0 6% 5.2 0% 0.0

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 36

| Appendix A |

Table A6: 2020 rain tank peak results under all use 2020 Summer % of Average Date of peak and order of peak day (1 to 5) summer summer 1 2 3 4 5 all use all use 19/02/2020 18/02/2020 20/02/2020 4/02/2020 11/02/2020 demand demand supplied supplied Tank size Development type (ML/d) % ML/d % ML/d % ML/d % ML/d % ML/d Small Large Lot 31% 0.5 4% 0.1 4% 0.1 4% 0.1 32% 0.6 4% 0.1 Single House 12% 2.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Terrace Housing & Apartment Buildings 11% 3.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Housing 8% 2.3 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Suburban 8% 6.9 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Medium Large Lot 31% 0.5 4% 0.1 4% 0.1 4% 0.1 32% 0.6 4% 0.1 Single House 17% 2.9 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Terrace Housing & Apartment Buildings 11% 3.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Housing 10% 2.7 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Suburban 10% 8.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Large Large Lot 47% 0.8 32% 0.6 32% 0.6 32% 0.6 49% 0.9 32% 0.6 Single House 27% 4.5 6% 1.0 6% 1.0 6% 1.0 6% 1.0 6% 1.0 Terrace Housing & Apartment Buildings 12% 3.1 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Housing 10% 2.8 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0 Mixed Suburban 10% 8.4 0% 0.0 0% 0.0 0% 0.0 0% 0.0 0% 0.0

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 37

| Appendix A |

Appendix B – Annual average yield plots for scenarios 1-4

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 38

| Appendix A |

Appendix B Annual average yield plots for scenarios 1-4

Figure B1: Scenario 1 rainwater tank annual average yield at 2055 - 23% of properties by 2055

Figure B2: Scenario 2 rainwater tank annual average yield at 2055 - 31% of properties by 2055

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 39

| Appendix A |

Figure B3: Scenario 3 rainwater tank annual average yield at 2055 - 57% of properties by 2055

Figure B4: Scenario 4 rainwater tank annual average yield at 2055 - 66% of properties by 205.

Waikato River Water Take and Discharge Proposal – Board of Inquiry | 40