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Rain Harvestingby Lawson SchallerRain water harvesting has been around for centuries all over the globe. After all, some of the highest quality water is delivered to your roof top for "free." Rain harvesting on the Central Coast is being done and is suitable for many applications. Here one must have large storage capacity to contain enough water to carry through the extended dry season. A 1000 square foot roof will capture approximately 640 gallons in a 1" rain storm. A 2000 square foot roof can capture approximately 25,000 gallons in a 20" rainfall season. That is a lot of water. There are folks who live entirely off of rain harvesting. However, even modest levels of rain water harvesting helps support our aquifers. The concept is relatively straight forward. The first storm of the season requires a first flush for your roof. In addition to screening or filtration, there is a device that you connect to your gutters and it provides, automatically, for the first flush. It allows the rain to clean the roof of contaminants (bird waste, leaf debris, dust, etc.) and divert the water and the contaminants away from the main storage tanks. After the first flush the rain passes through a filtration system before entering the storage tank. The filtration requirements vary depending upon your needs. Water for irrigation requires much less filtration than water for drinking. There are a number of types of filters to choose from. The type of roofing you have (metal, clay, composite, etc.) can impact the quality of your water. There is concern of leaching from composite roofs. The tanks need to be properly screened to keep out mosquitoes and other insects. Screening also prevent rodents and birds from entering the tank. You also want to have a series of bends in the line to keep daylight out of your tank (and no translucent or opaque tanks). Install a spigot or valve near the bottom of the tank to gravity feed the water. You also want an even lower valve or outlet at the bottom to flush the bottom of the tank of sediment, debris etc. Having a proper overflow set up is very important. The space availability for tanks on your property needs assessing. There are an increasing number of choices in tanks. Types of materials used include steel, metal, fiberglass, plastic/poly's, and ferro-cement. Also, in shapes, we are seeing more "slim line" or narrow profile tanks that can work in narrow areas alongside homes or buildings. There are underground tanks and also underground "modules," vaguely similar to milk crates that create voids that allow water storage. The modules provide structural integrity and can be installed in different depths, widths, and lengths. There are "pillow" or bladder tanks that are flexible membranes that might be used in a crawl space or under a deck. With ground water dropping in SLO County, and many water basins in trouble, it is making more and more sense to capture and use rainwater. It also helps with minimizing storm water runoff. Storm water runoff runs down the streets and curbs and accumulates contaminants as it rushes to surface waters – nearby streams, lakes, estuaries, and the ocean. Residential homeowners can harvest significant quantities of rain water. People on small acreage with barns or other out buildings have the roof capacity to harvest tremendous amounts of rain water. This is only a brief overview of rain harvesting. Contact a professional for guidance, consulting, and installation.
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