The primary storage portion of a rainwater harvesting system is where the water is conveyed to and stored until it is discharged to the end-use. The storage system can be modular or a single unit, can be located above or below-ground and can be made out of a variety of materials, generally either concrete, metal, plastic, wood or some combination those listed. The size, shape within a given material category can vary widely, but a following is a summary of the common materials used in aboveground tanks and cisterns. No matter the tank material or size, manufacturer-recommeneded-guidelines should be followed for tank installation and maintenance and for proper design of foundations of the tanks and cisterns. In order to prevent algae blooms inside the tank, opaque materials, gaskets and caulking may be needed to block all light from entering. If colder or cooler water is desired, position tank away or out of direct sunlight. Some materials, such as some types of plastic, are more susceptible to UV degradation and fluctuations in temperature. Polypropylene Polyethylene FRP Stainless steel with gaskets Coated steel Galvanized and alumunized steel with flexible inner-liners Cast-in-place Precast one-piece Precast modular Ferro-concrete tanks (tanks where concrete is sprayed on the frame) Synthetic fabric construction As before, tanks shapes and sizes can vary within a material category. Plans for accommodating existing and future subsurface utilities and integration with the conveyance system must be approached early on in the design process. Manufacturer's recommendations for installation, foundation design, water table analysis, buoyancy anchoring and backfilling should be followed. Ensure that access to the below ground tank is not in any way inhibited or discouraged by the placement of the tank. Doing so may discourage or cause the later inability to properly enter the tank for maintenance and inspections. Ensure that during construction, contamination and runoff does not enter the tank, or if so, ensure that it is cleaned before first use. Polypropylene Polyethylene Coated steel Galvanized and aluminized steel Cast-in-place Precast one-piece tanks Precast modular
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