Water Harvesting

How to Harvest Rainwater

Water harvesting systems can range from the simple to the complex, depending on your needs and budget. Whether you're building a new home on a single lot, designing a major subdivision, or just making a few improvements around your yard, water harvesting can be easily incorporated into your plans.

It can be helpful to think of a harvesting system as having four main components:

1) Rainwater Collection

2) Storage

3) Distribution

4) System Maintenance

 

Rainwater Collection

You can capture rainwater from any rooftop area, patio, driveway or other impermeable surface. Make sure that collected water is kept at least three feet away from the foundation of your house. The amount of water you'll be able to harvest depends on the size of your catchment area. To determine the amount of water you can collect, multiply the square footage of your catchment area times the amount of rain received each year in feet (about one foot of rain per year in Pima County). Next, multiply that value by .90 to account for evaporation and other losses, and then multiply this result by 7.5 to determine the number of gallons. As an example, a 1,000 square foot catchment area will yield about 6,750 gallons of water per year (1,000 x 1 x .90 x 7.5 = 6,750).

 

Storage

Storage systems can vary in complexity depending on your needs. An effective system can involve a 55-gallon drum fed by rooftop gutters and downspouts. A more involved system might include buried cisterns, plumbing and a timed watering system. Debris and leaves should be filtered before storing the water by placing screens over gutters or downspouts. Water kept in tanks or cisterns should also be covered to minimize algae growth and eliminate the potential for mosquito breeding. Placing floating lids on storage tanks is an effective solution.

 

Distribution

Gutters and downspouts or berms and swales can be designed to catch rainwater and distribute it directly to landscape plants or into tree wells. Rainwater can also be directed to rock-lined trenches or perforated pipes and allowed to infiltrate into the soil. Many people store harvested rainwater and then distribute it later through their regular drip irrigation system.

System Maintenance

Water harvesting systems require occasional maintenance, but this is easily accomplished. Debris screens over gutters should be cleaned periodically and storage tanks should be drained and cleaned when it is convenient to do so.