Rainwater harvesting: your water supply from the sky

If you are like me, you are doubtless happy after the recent rains. This is especially true if you have a rainwater harvesting system and rain water tanks on your property.

Rainwater harvesting can be as simple as a small inexpensive drum or rain barrel positioned to catch runoff from a valley on the roof, or as complex as a five-thousand gallon reservoir or water tank with a sophisticated filtration system to provide indoor water. Regardless of the level of complexity you are comfortable with; all rainwater harvesting systems have the same basic components.

The first point of contact for the system will be a catchment surface. This is usually a roof. Roof materials that contain lead such as some wood shingles or flashing should be avoided. Standard composite shingles and metal are excellent surface materials for catching rain. The shape and slope of your roof have little direct effect on the amount rainwater you can catch. The footprint of the area under the roof is more important for determining the size of your catchment area.

You will need a method of carrying the rainwater from the roof to a holding area. Few homes in West Texas have gutters but they are critical to taking advantage of the water that falls on the roof. Properly supported gutters should be wide enough to catch rain with the force of a 100-year storm. Wide gutters are often more efficient but material costs may increase as gutter width increases.

A storage area is needed for holding the rainwater. Downspouts can be directed into rain gardens in the landscape or water tanks made of synthetic materials. The most common type of water storage tank is made of plastic or polyethylene. Transparent water tanks should be painted. Light finding its way into the water tank may cause the growth of algae.

Large water tanks should have a secure top to prevent anything except water from entering it.

How much water can you expect to collect in West Texas? A 1,200 square foot roof can catch just more than 750 gallons of water from one inch of rainfall (rainwater harvested = square feet of surface area times inches of rain times 0.63).

If we ever receive our typical 14-inches of rainfall in a given year, a properly designed system with a 12-hundred square foot roof could capture more than 10000 gallons of water.