Rainwater harvesting is a method for collecting and storing rainwater on-site for future use. Landscape irrigation accounts for 30-50 percent of total potable water used across many Texas communities (Texas A&M Agrilife Extension). Collecting and using rainwater is a way to preserve potable water for human consumption. Also, plants prefer rainwater to treated drinking water because rainwater it has a near neutral pH levels, and is free of salts and other minerals that can harm root growth.
There are two categories of rainwater harvesting systems; active and passive.
Active rainwater catchment refers to systems that actively collect, filter, store and reuse water, typically through a system of rain gutters, barrels or cisterns. They can also incorporate pumps and filters. Rooftops are often part of active rainwater catchment since they can generate large volumes of runoff which, when discharged to paved surfaces and landscaped areas, can generate large pollutant loads. Rainwater harvesting systems can capture this runoff before it is discharged, thus preventing pollution while also putting the captured water to beneficial use, such as landscape irrigation or cooling water.
Passive harvesting systems incorporate no mechanical methods of collecting, cleaning or storing water. Instead passive systems are created from berms, swales, basins, or rain gardens that direct water towards low points in the landscape where water gathers and then soaks into the ground.
Basic components of active system:
Gutters and downspouts
Leaf screens, first flush diverters, roof washers
Treatment / purification
Basic components of passive system:
Rocks to slow water down or provide barriers
Rain gardens or rainscapes are passive systems - these low areas absorb and filter rainwater runoff that comes from roofs, sidewalks, and driveways. Rain runs off the hard surfaces, collects in the shallow depression, and slowly soaks into the soil. They are usually planted with colorful native plants and grasses.