Sustainable Building Technical Manual - Etn-presco.net

use vary by locality. If rainfall is to be used for potable or irrigation purposes, localhealth codes may require backflow prevention devices in order to avoid any risk ofcontaminating the public drinking-water supply. Check with local health-code officialsfor guidelines for your area.❑ Design an appropriate harvesting and storage system.The capacity of rainwater harvesting to meet water needs depends on the amount ofrainfall in an area, the size of the collection area, the size of the storage area, and waterneeds. One inch of rainfall translates to 0.6 gallon of rainwater collected per squarefoot of roof area. Basic components of a rainwater-collection system include the catchmentarea (usually the roof), conveyance system (guttering, downspouts, piping), filtrationsystem, storage system (cistern), and distribution system. The highest cost inmost rainwater-collection systems is for water storage.– Use appropriate roofing materials. The best roof materials for catchment are metal,clay, and concrete-based (such as tile or fiber cement). Asbestos roof materials arenot suitable for potable collection because grit can enter the system. Use of asbestosroof materials may not be permitted under local building codes. Lead-containingmaterials such as flashing should not be used in catchment roofs.– Install gutters and downspouts sized for the roof size and rainfall intensity. Installscreening so that leaves and debris do not enter the cistern, as well as a “roof-washer”device to divert the first flush of water after a rainfall, preventing it from enteringthe cistern.– Construct cistern storage. Cisterns may be constructed from a wide variety of materials.Prefabricated cisterns in steel or fiberglass are available, but tend to be quiteexpensive. Cisterns also may be constructed on site from concrete, ferro-cement,stone, or compressed earth. Cistern interior surfaces must, of course, be watertight.Health codes require them to be covered to prevent mosquito breeding and contamination.To prevent algae growth, which occurs with exposure to sunlight, useopaque materials only.❑ Filter and/or treat rainwater to use it as an irrigation source.Simple filtration with graded screens and paper filters can filter harvested rainwater foruse in irrigation. With additional treatment, rainwater can also be potable.Landscaping❑ Plant native or well-adapted species.In areas with low rainfall or seasonal droughts, up to 60 percent of total seasonal waterusage can be attributed to irrigation. Typical urban landscapes consist of non-native orunadapted plant species, lawns, and a few trees. Non-native plants increase demandsfor water, especially during the growing season, thereby depleting local water suppliesand driving the need for larger-capacity centralized facilities that may lie dormant duringperiods of low water use.Native plants have become adapted to natural conditions of an area such as seasonaldrought, pest problems, and native soils. Landscape designs that emphasize nativetrees, vines, shrubs, and perennials also help maintain the biological diversity of aregion and preserve the character of regional landscapes.❑ Preserve native plant populations through careful site planning and protection ofexisting vegetation.Protect trees by avoiding cut-and-fill in root zones (at a minimum, the area beneaththe tree’s outermost branches) and preventing heavy equipment from disturbing thearea around and under them. The best way to protect existing vegetation is to fencegroups of trees off (Figure 5).