Basic Components of a Rainwater Harvesting System

Rainwater systems come in all shapes and sizes, from simple catchment system under a downspout to large above and/or underground cisterns or water tanks with complex filtration systems that can store thousands of gallons of water.

The above diagram is from RainHarvest in the USA but the principles apply throughout the world.

Most rainwater collection systems are comprised of the following basic components:

• Catchment surface – rooftop or other raised solid surface. The best catchment systems have hard, smooth surfaces such as metal roofs or concrete areas. The amount of water harvested depends on the quantity of rainfall, and the size of the surface and the slope of the catchment area.
• Gutters and downspouts – also known as distribution systems that channel the water from the catchment area to a holding container such as a barrel, cistern, reservoir, water tank, planted area, etc.
• Leaf screens – a screen that removes or catches debris.
• Roof washers – a device that diverts the “first flush” of rain before it enters the storage tank. Most rainwater suppliers recommend that the “first flush” of water is diverted to an outside area of the storage system, since the catchment surface may accumulate bird droppings, debris and other pollution.
• Storage tanks – In general, the storage tank is the most expensive component of a rainwater harvesting system. There are numerous types and styles of storage tanks available. Storage can be accomplished using above-ground or underground water tanks or water reservoirs. Storage containers can be made from galvanized steel, wood, concrete, clay, plastic, fiberglass, polyethylene, masonry, etc. Examples of above-ground storage include; cisterns, barrels, tanks, garbage cans, above ground swimming pools, etc. Storage tank prices vary based on different variables such as size, material and complexity. To inhibit the growth of algae, storage tanks should be opaque and preferably placed away from direct sunlight. The water tanks should also be placed close to the areas of use and supply line to reduce the distance over which the water is delivered. Also consider placing the storage at an elevated area to take advantage of gravity flow. The water tank should always be placed on a stable and level area to prevent it from leaning and possibly collapsing.
• Delivery systems – gravity-fed or pumped to the landscape or other end use areas.
• Purification/treatment system – needed for potable systems to make the water safe for human consumption. Please check with your local health department for information on filtration systems and certification requirements.

Source: The City of San Diego (gov.) (Excerpt)

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