Rainwater harvesting is one strategy to reduce domestic water use. Harvesting rainwater can lead us 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, 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
The 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 and into the storm drain. In some cities storm drains are connected to the sewer treatment plant, and heavy rains cause the sewer plant to overflow raw and partially treated sewer into lakes or rivers. Other cities connect storm drains to underground creeks, and the polluted water runs straight into the lake 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.
The third source of rainwater is the roof. Even in areas with low rainfall there’s enormous potential for harvesting rainwater. A 1,000 square foot house can collect about 2300 litres per inch of rain! So in an average year with 23 inches of rain in Toronto, that small roof could collect 1,380,000 litres.
The rain catchment system
A water catchment system for roof rainwater is simple, and can store water for outdoor irrigation.
- 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 algae 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’re low cost, and can be installed along houses, under decks, or in other unused spaces.
There’s 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.
Ceramic drinking water filter: This highly-effective, passive filter removes pollutants and pathogens including viruses from drinking water. 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. 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.