Department of Water Resources
A daily compilation of significant news articles and comment
June 2, 2008
4. Water Quality –
Tips on capturing rainwater
The San Francisco Chronicle – 5/31/08
Philip S. Wenz
Until recently, many cities have required that homeowners connect their roof downspouts to their municipal storm water sewers to control flooding and to deliver rainwater - which is polluted with roof dirt and bird feces - to sewage treatment plants. But as cities have grown, their storm sewers, which are often combined with sanitary sewers, are becoming loaded to capacity and can flood during heavy raAins, dumping sewage into streets and waterways.
Meanwhile, the threat of a long-term drought hangs over much of
These flood/drought conditions are leading to a reversal of previous policies, and many cities, including
Although rain barrels, if widely used, will help relieve sewer overloads and are relatively inexpensive and easy to install, they don't store enough water to last for long in the Bay Area's dry season. Storage tank systems, which can be installed either by homeowners or by professionals, can serve as a hedge against future water shortages and add value to your property.
Storage tanks are not filled just once during the rainy season then emptied in the summer. They are filled during spring and fall rainstorms, used for watering in the intervals between storms then refilled during the next storm. Thus the amount of water that can be applied to your landscaping far exceeds your tank's nominal capacity.
Ideally, your storage tank would be big enough to meet all your non-potable-water needs for the entire dry season, but such a tank might be too expensive and too large for your yard. Also, it's difficult to quantify landscaping needs because of the many variables involved. It's probably better, then, to start by installing a moderate-size tank, say in the 500- to 1,000-gallon range for a "typical" quarter-acre lot, and plan to add a second tank if needed. (There will be plenty of water to fill the tank(s). A 2,000-square-foot roof in the Bay Area can shed as much as 24,000 gallons of water per year.)
Tanks can be built on-site or purchased. City lot-size tanks are cheap enough - $400 to $700 for a 750-gallon tank, for example - so that it's probably more practical to buy a good-quality fiberglass, polyethylene or metal tank than build one of wood, concrete or masonry. If appearance is an issue, you can disguise the tank behind a fence or arbor. (Tanks should be dark to prevent algal growth, so they should be opaque or covered.)
Tanks are best placed aboveground: Underground-rated tanks cost about twice as much as surface tanks, excavation adds more expense and maintenance is difficult. Also, underground tanks need electric pumps to deliver their water, while most surface tanks can be positioned to take advantage of gravity.
Seismic considerations are important in tank design and placement. Water is heavy - 1,000 gallons weighs more than 4 tons - and tall, narrow tanks are less stable than squat tanks. Decks need reinforcement to support water tanks, and all ground-level tanks should sit on reinforced concrete pads and be fitted with earthquake bracing.
Tank water should be as clean as possible, so water from the rainy season's first good storm, which will flush a whole summer's worth of dirt off the roof, should not be stored but should be returned either to the ground or to a storm sewer - whichever your city requires.
More dirt will settle on your roof between storms, so subsequent rainwater should cleaned in a "first-flush washer" that separates the initial surge of water from the water destined for storage (see drawings). First-flush washers, filters and other components are available from numerous vendors (try an Internet search for "rainwater catchment"), and a lively discussion about the advantages and disadvantages of the various products can be found on the Web.
In most cities, you'll need a permit to install a rainwater catchment system - there are seismic and health issues and plumbing and building codes involved. Check with your building department before designing your system.
You'll probably need to consult with a structural engineer and might need a carpenter or plumber to help you. But if you are handy and willing do some research and planning, there's no reason you can't design and build a rainwater catchment system for your ecological house. #
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/05/30/HO3210LJS2.DTL
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