G2148 Management: Rainwater Harvesting in Residential-Scale Landscapes Kelly A. Feehan, Extension Educator; Katie A. Pekarek, Extension Stormwater Educator; Bobbi A. Holm, Extension Educator; David P. Shelton, Extension Agricultural Engineer; Steven N. Rodie, Landscape Horticulture Specialist; and Thomas G. Franti, Extension Surface Management Engineer rainwater to be suitable for potable uses like drinking, This NebGuide provides an overview of rainwater cooking, or bathing. This NebGuide only deals with harvesting systems and the use of collected rainwater for residential-scale rainwater harvesting systems and the use landscape and other outdoor non-potable uses. of captured rainwater for landscape irrigation and other outdoor, non-potable uses. Rainwater harvesting refers to the collection of - water to maximize its environmental and landscape value. Why Harvest Rainwater? Harvesting rainwater reduces stormwater runoff volume and velocity and can provide an alternative water source Rainwater harvesting has been practiced for centuries and to help conserve potable water supplies. There are typi- was once a primary method of obtaining water for domestic cally three components in a use. Increasing water de- rainwater harvesting system: mands, water use restrictions, 1) collection; 2) transport; new stormwater management and 3) infiltration or storage regulations, and the growth and use. of low-impact development Collection generally oc- (LID) and “green building” curs from rooftops or paved practices have sparked re- surfaces. The collected rain- newed interest in rainwater water is then transported, harvesting. often through downspouts or In most communities, swales, and temporarily held rainwater is treated as a in a storage device for future nuisance and is moved off use. The rainwater also may developed sites as quickly be diverted to planted areas, as possible by street gutters, such as a , for in- storm drains, and other means. and use by plants, or Public water supplies, treated directly infiltrated into the to standards, through permeable paving or are used for virtually every an underground structure such end use including toilet flush- as a dry well. Rainwater harvesting systems are classified as ing, car washing, and landscape irrigation. Although currently green infrastructure which is targeted at collecting stormwater the norm, it is not a sustainable practice to continue using to infiltrate and/or store for later use. water treated to drinking water standards for non-potable uses. Harvested rainwater can provide an alternative source to help Rainwater Uses reduce demand on drinking water supplies. Rainwater harvesting also has an important role in Harvested rainwater can be used for potable or non- urban stormwater management. Towns and cities with potable purposes. Non-potable uses include landscape or populations greater than 10,000 are required to reduce the container plant irrigation, car washing, and toilet flush- amount of stormwater runoff and associated pollution. Us- ing. The use of rainwater in a domestic plumbing system, ing appropriately sited and installed rainwater harvesting even for toilet flushing, requires some form of treatment. systems throughout a community will help municipalities Appropriate filtering and disinfection are required ­for with these requirements. Pollution from Runoff Rainwater Harvesting Systems With Greenspace

When rain falls on impervious surfaces such as rooftops, Using greenspace to capture and infiltrate stormwater parking lots, streets, driveways, and compacted , large can be as simple as directing downspouts to planted areas quantities of runoff are generated. This water is generally or constructing small berms and drainage channels (swales) directed into storm drains and conveyed directly to a stream, to direct rainwater to planted areas such as shrub borders river, or lake without any treatment. In highly urbanized areas, or tree rows. Eliminating direct flows to streets and storm only minimal amounts of precipitation soak into the soil due drains lessens runoff volumes during storms. However, to the high percentage of impervious surfaces. This results rain gardens, bioretention gardens, bioswales, and other in a high volume and velocity of concentrated stormwater planted areas installed specifically to infiltrate stormwater runoff that can lead to flooding and polluted surface . will have greater impact. Runoff pollution occurs as stormwater flows over surfaces, A rain garden collecting contaminants like sediment, fertilizer, pesticides, is an ornamental bacteria, plant debris, metals, fuel, oil, and others. Because garden planted in a most stormwater runoff is not treated before it is discharged shallow depression to a waterbody, contaminants are carried directly to surface that is designed waters. In addition, runoff to storm drains represents a lost to hold water for opportunity to collect and use rainwater as an alternative a short time (12- water source. 48 hours) before it drains away. These Water and Use typically have berms on three Water is essential to and has no substitute. Population sides and are lo- Figure 1. Rain garden (Hastings, Neb.) growth, climate change, and other factors are placing greater cated where rainwater from a roof or pavement can be easily demand on supplies. This increased demand, directed to them. Water collected in a properly designed rain combined with , emphasizes the critical need garden will infiltrate into the soil for up to 90 percent of all to efficiently use potable water and to increase the use of rain events. However, during heavy rain events, water can alternative sources for non-potable purposes. leave the garden as via overflows designed In most of the United States, easy access to an abundant, into the berm. The plants and soil in a rain garden facilitate safe, and relatively inexpensive supply of potable water has infiltration and evapotranspiration, as well as provide natural been the norm since the last half of the 20th century. Public pollutant filtering Figure( 1). water supplies are required to meet minimum standards de- Bioretention gardens are also ornamental and planted fined by the U.S. Environmental Protection Agency’s Safe in landscape depressions designed to hold and infiltrate Drinking Water Act. Achieving these standards often involves stormwater runoff within a short period of time. In contrast some form of treatment, and the water must then be delivered to rain gardens, bioretention basins are usually larger, have to users through a distribution system. These processes can engineered soils (typically a mixture of sand and compost), be energy intensive. Even so, this high-quality water is used and an underdrain system (gravel bed and perforated drain). for virtually every end use even though lesser quality water Collected water infiltrates into the soil or is discharged through would suffice for some applications. It is estimated that 40 the underdrain into the storm drain system after being filtered percent or more of home water use is for landscape irrigation by plant roots and soil (Figure 2). during the growing season. Plants do not require water that has been treated to drinking water standards. Untreated rainwater is suitable for plant and landscape irrigation. PondingPonding Area Area Forebay Benefits of Rainwater Harvesting

Finding and using alternative water sources for - scape irrigation is needed for sustainable water and energy management now and in the future. The benefits of rainwater 18” – 24” harvesting include: 18” - 24”

• A relatively inexpensive supply of water that needs IInfiltrationnfiltration Cell Cell little or no treatment for most landscape uses. • Decreased volume and velocity of stormwater runoff Sub-drainSub‐drain Pipe pipe leading to reduced stream bank erosion, decreased BIORETENTIONBIORETENTION GARDEN GARDEN CROSS SECTION CROSS SECTION flooding, and fewer pollutants entering waterbodies. Figure 2. Bioretention garden cross section • Potential reduction of municipal stormwater manage- ment and infrastructure costs. • Reduced demand on public potable water supplies and A swale is a broad, shallow, gently sloped channel used lowered energy consumption for water treatment and to convey and infiltrate stormwater. Swales may be lined distribution. with vegetation, gravel or rocks (dry stream bed), compost, • Increased soil moisture and improved plant root growth rip-rap, or other material.­ They are designed to slow runoff for increased tolerance and less irrigation. water velocity, trap sediment and other contaminants, and • Potential recharge. promote infiltration. Vegetated swales are also referred to as bioswales, enhanced swales, grassed swales, or swales (Figure 3). Stormwater planters are con- tainers typically in- stalled at or beneath Figure 6. Permeable pavers (left); Pervious concrete (right) street or sidewalk level in which trees Figure 3. Bioswale (Lincoln, Neb.) Rainwater Harvesting Systems with Storage Devices and other types of plants are planted. Rain barrels are small tanks that store runoff, usually from Runoff is directed a roof. Rain barrels are commercially available or adapted from into the planter box existing barrels, sit above ground, and typically have a capacity where it is filtered of 55-100 gallons. While rain barrels are a good introduction to by soil and veg- rainwater harvesting, etation and then they are limited in the discharged into a amount of rainwater storm drain system held. Small water through an over- storage units will flow or underdrain. fill quickly. For this This helps remove reason, an overflow pollutants and to move excess water slows the flow of away from build- stormwater enter­ ing foundations is ing a storm drain needed. Overflow system (Figure­ 4). water can be directed Green roofs Figure 4. Stormwater planter (Portland, Ore.) to additional linked are vegetated roof storage units, or ide- systems. They ally to a rain garden, commonly consist bioretention basin, or of drought-tolerant bioswale (Figure 7). plants, a layer of are Figure 7. Rain barrels with overflow to rain growing media, large (100 gallons garden (Hastings, Neb.) a root barrier, a or more) tanks for drainage system, storing collected and a waterproof rainwater. They can membrane on top be built above or of the roof deck. belowground and Figure 5. (Omaha, Neb.) Green roofs di- some have integrat- rectly intercept and absorb rainwater, provide insulation, ed pumping devices and moderate rooftop surface temperatures. They may (Figure 8). also extend the life of the roof membrane due to decreased Bladder tanks exposure to temperature extremes, weather, and ultraviolet are reinforced syn- light. Green roofs can only be installed on buildings with thetic bags supported the structural integrity to support the additional weight by a metal frame and (Figure 5). usually located be- neath a deck or porch Rainwater Harvesting Systems with Permeable Paving or in a crawl space. Dry wells are Permeable paving includes several methods and permeable under- materials used for patio construction and paving drive- ground structures or Figure 8. 6,000 gallon (Papillion, Neb.) ways, parking lots, and streets. Examples include pervious buried volumes of gravel that store and then slowly release concrete, porous asphalt, and permeable pavers such as captured rainwater into the surrounding soil. paving stones or bricks (Figure 6). Pervious hardscape Proper use and maintenance of storage devices is essen- allows water and air to infiltrate through the surface tial for safety. Some things to consider are covers to prevent material into soil or supporting material directly below. children or pets from climbing into the container; a secure, The design may include an underdrain system or an level base to prevent tipping of smaller containers; screening underlying reservoir, tank, or vault for additional water to prevent mosquito entry; and methods to carry overflow holding capacity. away from building foundations. General Steps to Selecting a Rainwater b. How the water will be used and how quickly it can Harvesting System be used. (Can the storage unit be emptied before the next predicted rainfall?) 1. Identify areas such as rooftops, paved areas, slopes, or c. How and where overflow would be directed when compacted soils from which rainwater could be har- there is heavy rainfall or when rainstorms occur in vested. close succession to one another. 2. Calculate the amount of rainwater that could be harvested 8. Before installing any rainwater harvesting system, become from each area. knowledgeable about: a. Determine the square footage of each collection area. a. Homeowner association rules. b. Multiply the square footage of the area by a rainfall b. State and local municipal codes and regulations. amount in inches; then multiply by 0.623 (a conver- c. Underground utility locating services. sion factor). d. Potential incentive programs for using rainwater Example: Harvested water (in gallons) = collection harvesting methods. area (square feet) x rainfall amount (inches) x 0.623. A 1,200 square foot roof would yield approximately Summary 750 gallons of water from a 1 inch rain. c. Estimate the square footage of the roof area that Renewed interest in rainwater harvesting has come about would drain to the downspout from which rainwater due to the ever increasing need to maintain and improve fresh would be collected to calculate the potential amount water . Rainwater harvesting represents an opportu- that will flow from that downspout. nity to conserve water and help protect surface waters from 3. Calculate the required capacity (size) a rainwater harvest- pollution and erosion. By using rainwater harvesting systems, ing system needs to be to catch and store enough rainwater it is possible to take advantage of rainwater as an alternative from the site. source of water for non-potable uses; thereby also conserving 4. Evaluate the amount of maintenance each rainwater har- drinking water and energy. vesting system requires and your willingness and ability to properly monitor and maintain the system. Resources 5. Based on these evaluations, consider which type of system (or multiple systems) to use for harvesting rainwater from Rainwater Harvesting (B-6153 05-08), AgriLIFE Extension. the site. Texas A & M System. To view, go to http://repository.tamu. 6. Analyze the suitability of the site specifically for the edu/search and enter B-6153 05-08 into the search box. harvesting system(s) being considered. Rainwater Harvesting Policies. Managing Wet Weather with a. Observe drainage patterns during rainfall events. Green Infrastructure Municipal Handbook. Environmental Understand where the water comes from and where Protection Agency. December 2008. To view, go to http:// it goes. Using natural drainage to direct and move www.dep.wv.gov/ and enter Rainwater Harvesting Policies water simplifies installation and may reduce costs. into the search box. b. Consider how rainwater will be moved from the Rainwater Harvesting: Soil Storage and Infiltration System collection area to an infiltration area. (B-6195 08-08), AgriLIFE Extension. Texas A & M Sys- c. Determine soil type and understand how water tem. http://repository.tamu.edu/search and enter B-6195 moves into and through it. Conduct a soil percola- 08-08 into the search box. tion test (refer to NebGuide G1472, Residential Harvesting Rainwater for Landscape Use. 2nd Edition, October Onsite Wastewater Treatment: Conducting a Soil 2004. Revised 2006. University of Arizona Cooperative Percolation Test) if an infiltration method is being Extension/Low 4 Program. To view, go to http://cals. considered. A soil infiltration method will not work arizona.edu/pubs/water/az1344.pdf. in every location. For example, infiltration methods Rainwater Harvesting: Rainscaping Iowa Landscapes for may not be appropriate for sites with slow infiltration Clean Water, June 2010. http://www.iowastormwater.org/. rates or where land slopes steeply or towards a build- ing. Minimum distances are also required between This publication has been peer reviewed. infiltration methods and building foundations, septic systems, and water tables to avoid possible structure damage or water contamination. UNL Extension publications are available online d. Determine if the installation will negatively affect at http://extension.unl.edu/publications. established trees, shrubs, or neighboring properties as a result of root disturbances or drastic changes to soil moisture and grade. Index: Water Management – Water Quality 7. If a storage method is to be used, determine: and a. How water would be moved from the collection site Lawn & Garden – Water Management to the storage tank. Issued May 2012

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