Rainwater Harvesting Basics

Rainwater harvesting is the accumulation and deposition of rainwater for reuse before it reaches the aquifer. Uses include water for garden, water for livestock, water for irrigation, and indoor heating and cooling of houses, as well as drinking water.

roof rain



Rainbarrel Water Collection in GardenHarvesting 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 in developed countries often is highest in the places where rain falls the least.

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 worldwide.

How to utilize rain water

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, preferably native, 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.

rainwater-harvestingStore the rain in cisterns and barrels

An obvious and easy source of rainwater is the roof. Even in areas with low rainfall there is an enormous potential for harvesting rainwater. For example, the roof  of a 100 m2 house can collect around 1000 liters per 10 mm of rain.

A water catchment system for roof rainwater is simple, and can store water for outdoor irrigation. Common parts of a roof collection system are:

  • Gutters: Roof water gathers in the gutters and runs to a pipe towards the tank.
  • Screen: The rainwater goes through a screen to remove leaves and debris, and then funnels into the top of a 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 100 lieters to tens of thousands of liters.

Ceramic gravity-filterIndoor use

In for example Australia, rainwater cisterns supply potable water to thousands of homes. All around the world it’s becoming more common for people to use rainwater indoors for non-potable uses. These systems can reduce or eliminate the use of municipal or well water. Most household rainwater systems use a pump and pressure tank to pressurize water. Many countries however do not yet 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, research has shown that rainwater harvested using a well designed system and protect the water from direct light is safe to use for washing and other household use. Filtering only the small amount of water used for drinking with passive filters such as a ceramic filter or with slow sand filters, greatly reduces system cost, and offers an affordable solution for clean drinking water.

Slow Sand Filter Diagram

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