Rainwater Harvesting Systems 101
That which protects also collects
What we're talking about here is rooftops being multi-functional. The same roof surface that is keeping the rain off of your head or your stuff is a tool for gathering rainwater as well. A roof which is under clear air and without overhanging vegitation is well set to be a rainwater harvesting surface. In general the debris present on a well set roof are no major concern, certainly when compared with the potential contaminants on or in the ground. Certain types of roofing will work better than others for rainharvesting. Seamed sheet metal looks to be the best choice at this point. There are no shingling layers to trap debris. After many years of use, water tests have shown no concerning residuals from metal roofs. The amount of roof needed varies as to the annual rainfall and seasonal patterns. How much you can collect from any roof is always the same: 0.6 gallons per square foot per inch of rain. You can gather 600 gallons of rainwater from a one inch rain on 1000 square feet of roof. The square feet of a collection surface is measured flatly from edge to edge, so be sure to add the overhangs and not add for pitch.
A 6-inch seamless gutter can be made of copper, steel or aluminum by an installer in many locales. Gutters fitted continuously (without coupled sections) make for smooth, leak-free function and larger size/capacity allows for fewer downspouts. The ogee style can be fitted with heavy duty screens.
Now let's talk about how the roof and gutters connect to the water storage tank. First you need a component to screen out any organic matter. This helps to wash the roof by trapping the debris so that it will not enter the tank. Getting the rainwater moved from structure to storage is done with 4-inch plastic pipe and fittings. Connections can be made directly to tanks set next to or within a roof area. To have a tank set away from your house, a piping system must be constructed and the storage set up downhill from your roof. One 4-inch pipeline should be fitted for each 1500 square feet of roof surface. Storage tanks are made of a variety of materials. The choices include wood, fiberglass, polyethylene and steel. They can all be used for drinking as well as other purposes. The stored rain is in turn pulled out by an electric pump and supplied to points of use or to a pressure tank. A pressure pump and tank combo are required to push the rainwater evenly through the supply line. Rainwater ends up in a perfectly drinkable state with the use of in-line sediment and carbon filters and an electronic purifier to remove bacteria.
The technical stuff
Your rain system will perform with the highest efficiency if you do not leave out any of the steps or components. Starting with the clearest existing roof, section of roof or building another structure such as a pole barn in a less vegetated location will simplify the storing of relatively clear rainwater.
The SDR-35 grade of 4-inch PVC pipe and fittings is the industry standard for residential rainwater drainage. SDR-35 is lightweight, durable and economical making it a good choice for most home projects.The most direct and cost effective set-up is a long straight seamless-guttered eave with a single outlet/lead-in connected to a vertically mounted roof wash pipe.A wash pipe is a simple device that collects debris in the lower section as rainwater filters passively through a built-in stainless steel screen in the top. The debris is in turn flushed through a valve or clean-out at the bottom and the screen cleaned via an adjacent access. Connection from the wash pipe to the storage tank can be made directly into the tank top or tied into a pipe manifold using attached risers. Constructing a pipe manifold is similar to setting up a syphon.You must mount each wash pipe/riser 18 inches or more higher than the tank fill level.This difference in elevation creates passive lifting in each riser that pushes the rainwater through the manifold to the lower level of the storage tank input.