About rainwater harvesting

Sourcing the Rain

A swale catches runoff and lets it sink into the soil.A swale catches runoff and lets it sink into the soil.We who live in cities and towns, and we who eat food grown on industrial farms, depend on imported water for daily survival. Our water and the water that grows our food travels hundreds of miles to reach us. It is powered by mountain-leveling coal, mega-dam hydro-power, and deadly nuclear power. The infrastructures that bring us this water costs billions of dollars in public tax money and household utility bills.



Harvesting rainwater can reduce our need--and demand--for water transport systems that threaten the health of the water cycle and our local environments. Ironically, water use is often highest in the places where rain falls the least. But whether you live in the damp Pacific Northwest, the arid Mojave desert, the thunderstorm Midwest, or beyond, we almost all depend on problematic water infrastructures.

An 11,000 gallon (3 story) cistern collects rainwater at the University of Arizona.An 11,000 gallon (3 story) cistern collects rainwater at the University of Arizona.

Rainwater harvesting is one strategy in the greater scheme of reducing domestic water use. By harvesting rainwater, we can be led to dozens of other practices that bring us into greater sustainability. Growing plants that shade and insulate windows reduces energy use; increasing home food production reduces demand for wasteful water use in industrial fields. Above all, rainwater harvesting increases quality of life: ours, and that of life worldwide.

In arid climates and places with salty irrigation water rainwater flushes salts and chemicals out, allowing for long-term health and soil vitality.

On any house lot, there are three potential sources for harvesting the rain: Direct rainfall, street harvesting, and roof harvesting.

Design landscape to welcome the rain

The easiest rainwater source is that which falls on the yard. Proper placement of plants, trees, and water sources can turn the site into a water efficient system. Shape the surface of the soil to slow down runoff, raise paths and patios, and sink all planting areas to capture the flow. Choose plants--primarily natives--that can absorb and hold water in their root systems, or pass it down to the water table. This way, rainwater doesn't run off into the street, where it would be swept away with motor oil, into the sewer system or discharged directly into a local waterway.



Harvest runoff- curbcuts and bioswales

Sidewalk bioswale treats street runoff in Portland, ORSidewalk bioswale treats street runoff in Portland, ORThe second source of rainwater is the street. Streets aren't flat; they are typically graded so that water flows to the curb, down the block to a gutter, into the storm drain. In cities like San Francisco and Portland, storm drains are connected to the sewer treatment plant, and heavy rains cause the sewer plant to overflow raw and partially treated sewer into the bay or river. Other cities connect storm drains to underground creeks, and the polluted water runs straight into the bay or nearby river. By cutting curbs and digging sunken basins into the "right-of way" or "parking strip" area of the sidewalk, you can turn street rainwater from a problem to a resource. Diverted rain that falls on streets can nourish plants, protect creeks, and contribute to cleaner cities.


Storm water runoff flows into basin after the curb was cut.Storm water runoff flows into basin after the curb was cut. ..

Store the rain- cisterns and rainbarrels

The third source of rainwater is the roof. Even in areas with low rainfall there is an enormous potential for harvesting rainwater.

For example, the roof a 1,000 square foot house can collect around 600 gallons per ONE inch of rain! In an average year with 12 inches of rain in Los Angeles, that small roof could collect 7,200 gallons.

The rain catchment system

A water catchment system for roof rainwater is simple, and can store water for outdoor irrigation. 200 gallons of storage tucked next to a garage200 gallons of storage tucked next to a garage

  • Gutters: Roof water gathers in the gutters and runs to a pipe towards the tank.
  • "First Flush": The first rain of the year is the dirtiest as it cleans the roof. This water is directed away from the tank in a "first flush system" and the subsequent water continues to the tank.
  • Screen: The rainwater goes through a screen to remove leaves and debris, and then funnels into the top of the covered tank.
  • Storage: The tank is dark, to prevent algea from growing, and screened, to prevent mosquitoes from entering.
  • Irrigation: A hose attachment is located near the bottom for irrigation.

Rainbarrels are a popular way to begin rainwater harvesting, especially in urban areas; they are low cost, and can be installed along houses, under decks, or in other unused spaces.

There is a huge range of options for cisterns, large single storage tanks. They can be made from plastic, ferrocement, metal, or fiberglass, ranging in size from 50 gallons to tens of thousands of gallons.


Plastic cisternPlastic cistern Metal cisternMetal cistern Ferrocement cisternFerrocement cistern

  More photos of rain catchment systems:




Indoor use

Ceramic drinking water filterCeramic drinking water filterIn Australia, rainwater cisterns supply potable water to thousands of homes. In the US, it's becoming more common for people to use rainwater indoors for non-potable uses. These systems can reduce or eliminate use of municipal or well water during the rainy season, when outdoor irrigation is unnecessary. Most household rainwater systems use a pump and pressure tank to pressurize water. Many states do not have codes covering indoor rainwater use, and people seeking permits may be required to  filter and disinfect the water, increasing system cost and complexity. However, EPA and other research has shown that rainwater harvested using a "first flush" system and protected from light is safe to use for bathing and other household use. Filtering only the small amount of water used for drinking with passive filters such as the ceramic filter shown at left, or with slow sand filters, greatly reduces system cost, and offers an affordable solution for people needing clean drinking water.

Large-scale rainwater harvesting projects

  • A sumo-wrestling arena in Tokyo, Japan, stores rainwater in a large underground tank for toilet flushing.
  • The Frankfurt Airport in Germany collects rainwater for toilet flushing and irrigation.
  • Eggleton Services, a non-profit in Norfolk, Virgina, uses rainwater from the roof of a laundry facility in the washing machines.

Read about rainwater harvesting projects from around the world here.

See more US examples from the American Rain Catchment Systems Association (ARCSA) here.