Solutions Library Solution 5: Rain Harvesting Cisterns "By harvesting nature, we can create a natural beauty all of our own." -Kylin Fulton Tahoma School District Student Rain Harvesting Cisterns 70
Cistern: http://chesapeakestormwater.net/2009/11/permeable-pavement-design-specification/ What is a Rain Harvesting Cistern? Collecting rainwater from rooftops has been used for centuries to satisfy human needs. Today, Valley View Middle School in the Snohomish School District captures enough rainwater to flush 100% of its toilets. Collecting rooftop runoff can simulate the amount of water that is naturally utilized by a forest. Rainwater collection systems can provide multiple benefits such as 1 Reducing summer peak demand and maintaining summer instream flows by reducing residential and commercial surface and ground water withdrawals. 2 Reducing costly water distribution infrastructure by collecting water close to the end use. 3 Reducing combined sewer overflow events in urban areas. 4 Providing a sustainable source of potable water where groundwater and surface water is degraded. 5 Emergency backup water source if main supply is not available. 6 Reducing runoff in urban retrofits or redevelopment where space is limited. Rain barrels Are a type of rainwater collection typically used for storing a small amount of water, about 50 gallons, for garden irrigation. They provide a valuable educational tool to engage the public in water conservation. Cisterns are used for larger storage volumes ranging from 200 gallons to 5,000-10,000 gallons (typical for supporting indoor use). Text Excerpted from the 2012 LID Technical Guidance Manual for Puget Sound 71 Rain Harvesting Cisterns
How a Rain Harvesting Cistern works? Sloping Roof Existing Gutter Downspout (rerouted) Filter Overflow Drain Explanation of Diagram Rain falls on a sloped roof, falls into an existing gutter, travels though a rerouted downspout, passes through a screen-like filter, and eventually falls in to the rain harvesting cistern. Rain Harvesting Cistern Water Spigot Rain Harvesting Cisterns 72
This is How To Install a Rain Harvesting Cistern Step 1: Design with Math + - x 1 Rainwater collection systems should be sized according to precipitation rates, indoor and outdoor water needs, and the flow reduction required to approximate pre-development hydrology, or in other words, like a forest. In the Pacific Northwest the greatest amount of precipitation falls between November and May. These are the same months when human demand for water is lowest. June through October is relatively dry and demand, driven primarily by landscape needs, is greatest. To collect and remove adequate storm flows during the higher precipitation months and provide a reliable water source, large storage reservoirs or cisterns are required. In our region rainwater collection should be sized to store up rainfall in April and May to provide water as far into the summer months as possible. Step 2: Install the Cistern www.westernskycommunications.com 2 The cistern is the most expensive component of the collection system. It s going to be extremely heavy when filled with water so you need to have a very solid, very flat surface to serve as a foundation. Cisterns are commonly constructed of fiberglass, polyethylene, concrete, metal, or wood. They can be installed above ground, under a deck, or in the basement or crawl space, or even buried underground. If your cistern is on high ground you can use gravity to feed a hose bib at the bottom. If your cistern is not on high ground you will need a pump system to take the water to where you need it. Connect the downspout from your gutter to the top of the cistern. Install an overflow system to let water escape into a rain garden or natural area if your cistern gets too full. Screens should be installed in the top of each downspout. Screens installed on gutters prevent leaves and needles, but not fine debris such as pollen and dust from entering the cistern. If you plan to use the rainwater you have collected indoors you will need much more elaborate filters. Step 3: Maintenance tips Debris should be removed from the roof as it accumulates. Gutters should be cleaned as necessary (for example in September, November, January, and April. The most critical cleaning is in mid to late-spring to flush pollen deposits from surrounding trees. Screens at the top of the downspout should be maintained in good condition. Storage tanks should be inspected and debris removed periodically as needed. 3 cleanpromemphis.com/gutter-cleaning/ 73 Rain Harvesting Cisterns
Go Build It! Photos Sourced From: http://www.ecojoes.com/how-to-attach-a-homemade-rain-water-barrel/ Rain Harvesting Cisterns 74
Do the Math! + - x Determining the Size and Type of Your Cistern or Rain Barrel The catchment area is equal to the length times width of the guttered area. Average annual rainfall in the greater Seattle area is 37 inches. One inch of rain falling on one square foot of rooftop will produce 0.6233 gallons of water or approximately 600 gallons per 1,000 square feet of roof. Assume that the system will lose 10-25 percent of the total rainfall due to evaporation, initial wetting of the collection material, and inefficiencies in the collection process. Precipitation loss is the least with metal, more with composition, and greatest with wood shake or shingle roofing materials. How many gallons do you need to meet your irrigation needs? How many gallons will you need if you are using it indoors to flush toilets and wash clothes? How many weeks of dry weather will your cistern provide before it is empty? What about water pressure? It depends on how tall your cistern is or how many feet off the ground. Water pressure or head is calculated at.5 pounds of pressure for every vertical foot of head. Standard residential water pressure is 40-60 pounds per square inch. That s what s coming out of your garden hose. X Y Consider Roof Materials The roof material should not contribute contaminants such as zinc, copper or lead to the collection system. Rainfall present in the Pacific Northwest is surprisingly acidic and will tend to leach materials from roofing material. Enameled standing seam metal, ceramic tile or slate are durable and smooth, presumed to not contribute significant contaminants, and are the preferred materials for potable supply. Composition or 3-tab roofing should only be used for irrigation catchment systems. Composition roofing is not recommended for irrigation supply if zinc has been applied for moss treatment. Lead solder should not be used for roof or gutter construction and existing roofs should be examined for lead content. Galvanized surfaces may deliver elevated particulate zinc during initial flushing and elevated dissolved zinc throughout a storm event. Copper should never be considered for roofing or gutters. When used for roofing material, copper can act as an herbicide if rooftop runoff is used for irrigation. Treated wood shingles or shakes should not be used. MATERIAL 1 Metal MATERIAL 2 Ceramic Tile MATERIAL 3 Copper Do Not Use 75 Rain Harvesting Cisterns
Sample Cost Project: Tahoma Cistern The first step is to reroute your downspout into your rain harvesting cistern. You may need to purchase downspout elbows to get the proper angle into your cistern. Next move your cistern into place and make sure that it is on a stable, level footing. If the cistern is big you may want to hire a contractor to move it into place for you. Now arrange your newly rerouted downspout directly into the cistern so it can get filtered and collect water like it was designed to do. Spreadsheet of Costs Quantity unit price COST Excavation and Foundation Prep 56 sf 10.00 560.00 Purchase 1,500 Gallon Cistern 1 1,200.00 1,200.00 Connect downspout, overflow and spigot 1 500.00 500.00 total 2,260.00 Description of Cost The cost associated with rain harvesting cisterns tends to range widely based on the size and type of the cistern being installed. The cistern itself is purchased as a single unit and is the most expensive part of the job. Most cisterns come equipped with overflow drains, water spigots, a filter, or any other extra you might need. Some cisterns are linked into the water systems of nearby buildings, but those tend to be on high-end construction projects and are typically installed during the construction of the building itself. Most cisterns are only attached to the downspout of a building so there will be some small cost in rerouted that downspout. You may need to purchase downspout elbows to get the proper angle into your cistern. If the cistern is big, you may want to hire a contractor to move the cistern into place and reroute the downspout for you. If the cistern is small, you should be able to handle most of the installation yourself. Rain Harvesting Cisterns 76
Cool Applications Everywhere 77 Rain Harvesting Cisterns
The Best of the Best - Rain Harvesting Cistern Images Sourced From: http://www.belltown.org/news.php Beckoning Cistern - Vine Street - Seattle, Washington The aluminum cistern collects roof watershed from the 81 Vine Street building. Water is directed from the roof via downspout then through the extended index finger of an outstretched hand and into the 10 x 6 dia. cistern before eventually making its way down Vine Street to the Cistern Steps. The gesture of the outreaching finger suggests that of the Creation of Adam by Michelangelo from the Sistine Chapel in Rome. Source: http://www.bustersimpson.net/beckoningcistern/ Rain Harvesting Cisterns 78
SOILS TREES RAINGARDENS PERMEABLE PAVEMENT CISTERNS 79