What is it?
Rainwater Harvesting is the gathering, accumulating and storing of rainwater. It is collected primarily from rooftops, into catchment tanks. Rainwater harvesting systems can range from a simple barrel at the bottom of a downspout to multiple tanks with pumps and controls. The quality of rainwater can vary with proximity to highly polluting sources. However, in general, the quality is very good. The softness of rainwater is valued for its cleaning abilities and benign effects on water-using equipment. As an irrigation source, as one would expect, is the best water for plants.
How is it used?
Stored water can be used for non-potable purposes such as irrigating lawns, washing cars, or flushing toilets. Rainwater harvesting is also effective in reducing storm water runoff pollution. When rain falls, it is clean, but it immediately picks up pollutants from rooftops and pavement. This pollution is carried into storm drains and then into streams. Collecting stormwater from rooftops and directing it to storage tanks so it can later be used for irrigation or flushing decreases the volume and rate of runoff.
Rainwater harvesting systems designed to fill all the water needs of a home can be similar in cost to the expense of putting in a well. Operating costs for a rainwater system can be less. Rainwater collection systems designed to supplement the water needs of a home already on the city system for irrigation purposes can be costly. The primary expense is in the storage tank (cistern). In Oklahoma, the cistern size for irrigation can be large due to the high temperatures and extended dry periods in the summer. If the system is not counted upon as the only source of irrigating water, building as large a cistern as one can afford is often the measuring gauge for cistern size.
No permits required!
You don't need permits to use collected rainwater outside the house. When collecting rainwater at home, here is an easy way to estimate annual water supply:
Collection Area (sq. ft) x Rainfall (in/yr.) / 12 (in/ft) = Cubic Feet of Water/Year
Cubic Feet/Year x 7.43 (Gallons/Cubic Foot) = Gallons/Year.
For example, a 500 sq. ft roof that gets 36 in/yr. will produce 1,500 Cubic Feet or 11,145 Gallons of water per year.*
*PLEASE NOTE: this calculation is for horizontal areas and does not take into consideration system losses such as evaporation or leakage