Rainwater Harvesting on Campus

Texas A&M University recently opened the Mitchell Physics Building in College Station. This building, like all new construction on campus, is LEED certified. LEED, which stands for Leadership in Energy and Environmental Design, is a national rating scale that focuses on sustainable building practices. The Mitchell Building was built at the silver standard of LEED certification, and it includes rainwater harvesting.

Rainwater and air conditioning condensate are captured from the rooftop and sent to an underground cistern (diagram below). This water is then used to irrigate landscaping in the front of the building (picture upper right) and the roof-top garden (picture upper left). This is the University's first roof-top garden.

Cold Weather

If you live in a region that receives significant freezing weather in the winter, you may be concerned about storing rainwater. However, with proper planning and construction, you may have nothing to fear. Usually the most vulnerable location that is prone to freezing is the piping. Be sure to wrap any exposed piping in insulation and when possible bury them below the freeze line. It may also be helpful to plan for a "dry-line" system which has no standing water in the pipes. Valves, pumps, and treatment equipment should be protected in a pump house or insulated box. As for the tank itself, round tanks with straight sides do better than round tanks or corrugated sides. Insulation around the tank can be used in extremely cold regions, and you must make sure that the roof can handle a heavy snow load.

Keeping Our Streams Full

Constructing a rain garden is an excellent way to harvest rainfall that may otherwise become detrimental runoff. Generally a rain garden is a depression filled with plants that slows down stormwater and allows it to infiltrate into the soil. It is often referred to as a "passive" or "simple" rainwater harvesting system. Unlike "active" or "complex" systems, you are not using tanks, pipes, and pumps to collect and use water.

Many people can understand the benefit of reducing runoff that rain gardens provide. Slowing down the water's flow can prevent land from eroding and streets from flooding. However, there is a common misconception when it comes to the water's infiltration. Some believe that by preventing runoff, we are reducing a water source for river and streams.

The truth is in fact quite the opposite. Streams and rivers (especially in the West) receive a large portion of their flows from groundwater. This is called base flow and is why streams still run during droughts.

Rain gardens replenish aquifers with water which eventually contributes to streamflow. This may be delayed as it can take anywhere from days to decades for water to reach a stream after infiltrating into the ground.

A Good Foundation is Key

When planning the construction of a rainwater harvesting system, one of the most critical aspects to consider is the ground beneath the future tank. Water weights 8.34 pounds per gallon. This can add up to tremendous weight under a tank:









Two extremes to look out for are soils with high clay or high sand content. Having a large amount of clay in a soil can result in shrinking and swelling. This can result in shifting tanks or broken pipes. A large amount of sand may be prone to erosion around the base of the tank.

An ideal base for tanks over 500 gallons would be concrete. However, you can also place a layer of pea gravel over a clay base to lessen the impact of swelling.

Barrel Coverings

One concern of many who consider a rain barrel is the bright color and "industrial" appearance of the barrel. You can alter the appearance of a barrel by painting it or adding a decorative covering.

To paint a barrel, clean and lightly sand the outside. You can then add either a spray paint specific for plastic or a latex paint with brush. One color or fancy designs: the possibilities are endless. See this website for several creative barrels in Kentucky.

The decorative covering seen on the right can give you an old-fashioned-barrel appearance and is easy to assemble. Take 14 wooden fence pickets and cut them as long as your barrel is tall. Purchase 6 inch flashing and cut them into three strips that are 2 inches wide. Lay the pickets in a row (separated by an 1/4 inch) and attach the flashing. You can then attach the two ends and slip the covering over the barrel. Wooden coverings for the overflow and top can also be made from pickets.

Where does the rainfall go?

Besides providing a free source of water, rainwater harvesting is one tool landowners can use to reduce runoff. In this video, Billy Kniffen of AgriLife Extension demonstrates how various land uses contribute differently to runoff and infiltration.

Importance of Overflow

As I waded through the lake of a parking lot this morning, I noticed the incredible speed at which the runoff collected and found its way to the storm drains. This is often how many fearless drivers get caught during floods. The power of water is usually underestimated.

The same can be said about roof runoff. Especially with rain barrels, the power of the runoff is often underestimated when making an overflow. The overflow needs to be at least the same diameter as the pipe/downspout leading into the tank. If not, water can spill out of the top of the barrel and run down the sides. This concentrated spilling water has the potential to erode away or ruin the integrity of the ground beneath the barrel.

Pipes from the overflow should lead to another barrel or be directed to an area where the water can drain safely. It is recommended that this be at least 10 feet away from a building's foundation.

Another important step to remember is equipping the overflow outlet with a device to prevent the entry of pests. A 1/16" mesh screen will keep out mosquitoes. If larger pests, such as mice, are an issue, larger, more sturdy screen may be needed. Do not use one with openings larger than 1/4".