Eco Green Technologies and Insulation

     A rainwater tank (also known as a rain barrel) is a water tank which is used to collect and store rain water runoff, typically from rooftops via rain gutters.

     Rainwater tanks are installed to make use of soft rain water for home use, reduce mains water use and aid self-sufficiency. In arid climates, rain barrels are often used to store water during the rainy season for use during dryer periods. Tanks can also be used for retention of storm water.

     Stored water is used for flushing toilets, in washing machines, watering gardens, washing cars, and sometimes for drinking, if adequate care is taken that the water is not contaminated.

     Disadvantages of a rainwater tank include the initial upfront cost, especially where water charges are otherwise fixed. Occasional maintenance to the tank is also required, or the user runs a health risk if maintenance is not carried out.

     Widespread use of rain barrels also changes the amount of rainwater reaching the ground in a particular area and draining into streams. Depending on the climate, this either helps prevent erosion, sedimentation, and pollution, and can reduce the strain on stormwater drainage systems; or it could cause rivers to dry up and ponds to stagnate.

     Rainwater tanks may be constructed from materials such as plastic, concrete, and galvanized steel, as well as fiberglass which is rust and chemical-resistant. Tanks are usually installed above ground, and are usually opaque to prevent the exposure of stored water to sunlight, to avoid algal blooms.

     Tanks are also covered and have screen inlets to exclude insects, debris, animals and bird droppings. Tanks often come with a plastic inner lining to both increase the life of the tank and protect the water quality.

     Apart from rooftops, tanks may also be set up to collect rainwater from concrete patios, driveways, and other impervious surfaces.

     Sizes typically range in capacity from around 100 to 25,000 gallons. Smaller tanks, such as the plastic 55 gallon barrel are used in some cases. Larger tanks are commonly used where there is no access to a centralized water supply. Also affecting tank size is predicted rainfall and rainfall variability; the higher prices for larger tanks; intended use of rainwater and typical consumption for these uses; the area of roof draining into the tank; security of supply desired.

Rainwater collection from roofs can be calculated using the following formulas:

• 1 inch of rain on a 1000 square feet roof yields 623 gallons of water; or

• 1 millimeter of rain on a 1 square meter surface yields 1 litre of water.