EVALUATION OF MUNICIPAL WATER DEMAND AND RELATED PARAMETERS IN SOUTH AFRICA HJ van Zyl*, AA Ilemobade, JE van Zyl**, LC Geustyn*** School of Civil Engineering & Environmental Eng., Wits University, P Bag 3, Wits 2050. *[email protected] , tel: (011) 717 7153, fax: (011) 339 1762 **Department of Civil Engineering Science, University of Johannesburg, ***GLS Consulting ABSTRACT South Africa is a water scarce country that constantly strives to apply its available water resources in the most efficient and equitable manner. Different users vis-à-vis industry, domestic, agriculture and the environment, vie for the available resources and have to be awarded an equitable and adequate share to ensure sustainability in the long term. Proper water demand management in South Africa is thus of critical importance. Researchers, municipal engineers and engineering consultants require good and reliable data and design guidelines on water demand patterns and factors influencing water demand to achieve this aim. The most commonly used South African guideline for water demand estimation for municipal services design first published in 1983(2), is currently published in the document titled “Guidelines for human settlement planning and design” (1) commonly known as the “Red Book”. The water demand guideline provides upper and lower limits for consumer demands per stand (erf) size. In this paper, the authors analyse measured water demand data of more than a million stands (domestic and non-domestic) contained in the treasury data for a cross selection of South African towns and cities. From the initial results generated, this paper provides (a) a preliminary evaluation of the current domestic water demand guideline published in the Red Book and, (b) non-domestic water demand trends. The main conclusions of the initial results of the study indicate that the domestic demands of most of the users fall well within the upper and lower limit envelope curves of the guideline, although the bulk of the data points seem to cluster around the lower curve. With regards to non-domestic water demand the study found that the frequency distributions of average annual daily demand (AADD) for specific non-domestic user categories seem to have a log-normal distribution. Further work is currently underway with multiple variable regression analyses to better understand domestic and non-domestic demand in relation to parameters possibly affecting demand such as income levels, stand size, climatic conditions, geographic locations and other socio economic factors. INTRODUCTION As with most water-related research, the underlying and holistic motive of the research discussed in this paper is the conservation of a limited natural resource that is indispensable for human life. Proper planning and future water demand management is essential in an economically developing and water scarce country such as South Africa. A key input in water demand management and planning for municipal services is the estimation of present and prediction of future water demand. Water demand estimates are used to calculate peak water demand and sewer flows and thus determines municipal water and sewer infrastructure requirements, which in turn decide water authorities’ budgets and capital investment needs. This paper reviews the existing demand estimation guidelines commonly used in South Africa and possible factors influencing municipal water demand by analysing water consumption data extracted from municipal treasury systems for more than a million consumers from a cross-section of South African towns and cities. REVIEW OF THE EXISTING WATER DEMAND ESTIMATION GUIDELINES The estimation of water demands normally consists of estimating the population, multiplying by an average daily per capita use and then applying peak-to-average ratios, based on entire cities, to estimate peak demands (3). The most commonly used guideline in South Africa to estimate water demand is published in the document “Guidelines for Human Settlement Planning and Design” (1) or the so-called “Red Book” published in 1994 (4) and revised in 2000 and 2003 (1). The guidelines contained in the “Red Book” have remained largely unchanged since its first publication in 1983 as the “Blue Book” (2) taking its name from the ring binder in which it was issued. A significant proportion of the the “Blue Book” guidelines are applicable only to urban residential areas with access to waterborne sanitation. Although various revisions of the guidelines published in the “Blue Book” have occurred over the past twenty years, the guidelines relating to urban water demand estimation have remained largely unchanged. The only significant revision being that the most recent publication of the guidelines distinguishes between water demand (domestic and non- domestic) in developing and developed areas. The following definitions are given (1): • Developing areas are considered to be those areas where the level of services to be installed may be subject to future upgrading to a higher level • Developed areas are considered to be those areas where the services installed are already at their highest level and therefore will not require future upgrading. For domestic consumption in developing areas the guideline provides a typical consumption value and a range in litre/capita/day for communal water points, stand pipes, yard connections and house connections based on the level of sanitation. For developed areas the average daily water demand for domestic users (single residential stands) is based on stand size. Two envelope curves are given, an upper and a lower limit. With regards to non-domestic demand the “Red Book” indicates that it is extremely difficult to estimate and recommends that non-domestic water demands should be based on field measurements where possible. In its water supply guidelines, the City of Johannesburg also recommends that non-domestic water demands should be determined, where possible, from the City Treasurer’s records on actual water consumption(5). Although the “Red Book” recommends actual measurement rather than estimation, it does provide a range for demand estimation for certain types of non-domestic consumers located in developing and developed areas. There are however, a number of non-domestic user types not considered in the “Red Book” guidelines. Updated guideline curves for residential water demand estimation were published in 2004 by Jacobs et al (6). The updated guidelines are based on stand size, but take into account four different geographic regions and also provide separate estimation curves for township and suburban areas. Jacobs et al investigated nearly 600 000 domestic users country wide using municipal treasury data and found the “Red Book” guideline to be too conservative. Despite the fact that the work by Jacobs et al provides a much improved stand-size based guideline for estimating residential demand, it still has the limitation of being stand-size based and is limited to residential demand. This study addresses this limitation by including other types of demand (e.g. non-domestic) and parameters possibly influencing demand. METHODOLOGY Water Consumption Data Collection Water consumption data was collected and evaluated in order to determine possible relations between average daily water demand and other potential parameters (e.g. stand size, stand value, climate and socio economic factors) influencing demand. The overriding problem with studying water demand is that quality data is not readily available. Even a large logging exercise can realistically only reach a small proportion of users. Furthermore, a logging survey is expensive and therefore further limits the length of the monitoring period and the number of users monitored. This study considered municipal water meter readings to be an ideal source of water demand information, since the readings are taken on a regular basis by virtually all municipalities in South Africa. Possible arguments against using meter readings for studying water demand are: • It is difficult to access and extract water demand information from municipal treasury systems • Meter readings are not always taken monthly and are estimated for some months • Meter readings are not always accurate as meters clock over or meter replacements take place • Customer information such as address, income level or user type contained in treasury systems are not always accurate Until recently, this wealth of water demand information in municipal treasury systems was generally difficult to access. Actual meter readings were often hidden in complicated database setups or could not be directly or easily linked to user information. In most cases it was not possible to analyse data programmatically i.e. using a computer and software. However, the past decade has seen significant software developments that now enable engineers to abstract and analyse demand information from treasury databases for selected municipalities that have employed these software tools (6). One such a software tool is SWIFT®. This software allows a user to interrogate and access municipal treasury databases to obtain demographic data, stand characteristics (size and value) and recorded water consumption for individual consumer connections. A number of municipalities have implemented SWIFT® including Tshwane Metropolitan Municipality, Ekurhuleni, Johannesburg Water and most of the municipalities of the Western Cape. The existing databases cover years of consumption data for hundreds of thousands of users. This study therefore,