Sonoma County Rooftop Resource Inc.
| Rainwater Harvesting Rainwater harvesting is a gravity powered water collection process that allows rain water to be gathered and stored for use during dry months. In most cases, rainwater harvesting systems can be added to the existing drainage of any structure. Rainwater is then filtered and collected for reuse in nonpotable water systems i.e. irrigation, toilets, etc. The collection system consists of: a drainage system, filtration system, a cistern (or water storage tank), and in some cases a pump to distribute the harvested water. A structure with external drainage, or none at all, is ideal but any rooftop can be converted to harvest rainwater. Leaf screens are installed over the catchment system, and at the gutter / downspout connection. A first-flush diverter, which diverts a specified amount of water at the beginning of each rain event, is then fitted to the gutter. The first flush of storm water is usually more laden with debris / pollutants that have gathered on the roof surface between rain events. Diverter capacity should be calculated for each individual site based on roof size and location. A roofwash filtration system is installed directly before the cistern. The roofwash system generally consists of a container with one or two canister filters inside. This filtration is put in place to remove smaller debris and organic materials. Storage tanks range from plastic or steel cisterns to reclaimed containers such as 50 gal. steel / plastic drums. Storage tank capacity should be based on the surface area of the rooftop being utilized, rainfall patterns, available space, and the proportion of rainwater to municipal water use that is desired. Water harvested from rooftop catchment systems is nonpotable, commonly referred to as “grey water”. It is possible, though in most cases unpractical, to treat harvested water for use in potable situations. Generally the water is stored and used for irrigation during the dry months. Harvested rainwater is ideally used with drip systems or low pressure sprayers to irrigate landscapes. Benefits of rainwater harvesting include: Conservation of: potable water and the energy required to deliver and treat said water. Minimization of: stress on water delivery systems and the need for costly upgrades to water treatment facilities. Reduction of: storm water runoff, pollutants entering the watershed through runoff, and the thermal impact of runoff (affected by the urban heat island effect) to surrounding wildlife and vegetation. Rainwater harvesting can also easily be paired with photovoltaics (solar panels) to increase savings and benefits. The cost of rainwater harvesting systems varies based on the components used and the desired use of harvested water. |
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