What is Rainwater Harvesting?

All water is rainwater and if collected by rainwater harvesting can be used as potable water for drinking, cooking, bathing, or nonpotable uses such as landscape irrigation, livestock watering and toilet flushing.

Rainwater has numerous benefits, ranging from improved water quality, softer water, as well as reduced stress on underground water supplies.

Rainwater typically has very low hardness levels. Softer water means that you can reduce the amount of soaps and detergents used in your laundry, and eliminates the need for a water softener. Fewer minerals also saves wear and tear on your plumbing fixtures and pipes.

Captured before it hits the ground, rainwater is free of many pollutants that are in our surface and underground water supplies. According to the Texas Water Development Board, "almost always exceeds [the quality] of ground or surface water."

But after it hits the ground that rainwater seeps through the earth and rocks and picks up minerals and salts. In many cases it also collects other contaminants such as industrial chemicals, pesticides and fecal coliform bacteria found in the soil.

Consider these Facts:

• One inch of rain on a 2,000 square foot residential roof will generate 1,250 gallons of water that can be reused.

• That roof in an area that receives 30 inches of annual rainfall generates 41,000 gallons of reusable water.

• The average U.S. household with a 10,000 square foot lot will use up to 3,000 gallons of water weekly for watering the lawn, shrubs, flowers, and plants.

• Running a sprinkler for 2 hours can use up to 500 gallons of water.

• Seventy percent of water used at home is used outdoors.


The average American uses between 50 and 100 gallons of water per day for showers, toilet flushing, clothes washing, cooking, drinking and lawn watering. Switching to low flush, 1.6-gallon toilets, low-flow shower heads and faucets, front load washers and other water-saving devices, you may be able to reduce your water use by up to half.

Conserving water means that you will need less storage capacity, making it possible to buy a smaller and less expensive tank or cistern.

The basic concept of rainwater harvesting is pretty simple. Rainwater is mostly collected from the roofs of buildings. It flows down by gravity through the gutters and downspouts into a storage tank or cistern. From the cistern the water can be used in the landscape as is, or be filtered and then purified to become a quality source of drinking water.

Since most rainfall tend to occurs in large storm events, the ability to store collected rainwater and knowing how to size the system is very important.

You could design your own system.

The simplest catchment system is a barrel under a down spout. There are many companies that sell a barrel designed for collecting rainwater from a down spout and are usually designed to hold about 55 gallons of rain water for use outdoors.

All of the components for a larger rainwater harvesting system, except for the cistern, can be found in the plumbing section of any home improvement store such as Lowes or Home Depot.

Usually metal downspouts are replaced with PVC piping. Making them watertight, water can be carried by gravity to a cistern.

Several downspouts can be joined together into one larger main pipe leading to the tank. An inlet to the tank is installed as high as possible to maximize storage capacity.

That inlet can be on the side or the top of the tank. Just remember, the solid PVC piping system (downspouts) at the building must be at least 6 inches above the highest piping at the tank. This will allow the tank to fill to capacity.

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