March, 7 2006  Rainfall harvesting saves water for "not-so- rainy" days

By Carmon McCain, High Plains Underground Water Conservation District

Collecting rainwater from roofs and storing it for future use is a practical method to save water for “not-so-rainy days,” says Texas Cooperative Extension Water Programs Specialist Mike Mecke of Fort Stockton, who holds a dual appointment with the Texas Water Resources Institute at Texas A&M University.

Water conservation is becoming increasingly important in Texas as the state’s population is expected to double by 2050, while water supplies remain the same or decline due to decline in some aquifers.

“Given this fact, we must protect our surface and ground water resources from pollution and overuse. Rainwater harvesting is one way to maximize the benefits of precipitation,” says Mecke.

Early homes depended upon cisterns to collect water before windmills were put into use and electricity was provided to farms through the Rural Electrification Administration (REA) in the late 1930s and early 1940s.

While these early rainwater harvesting systems were dismantled and forgotten by younger generations, use of cisterns is still common in many portions of the world, including Australia, the Bahamas, and Hawaii.

Mecke says rainfall harvesting is “an old technology that is new again.” Current interest in this conservation practice is being sparked by increasing demand for a decreasing water supply, rising economic and environmental costs to develop new water sources, water quality issues, storm water runoff issues, and drought concerns.

Persons can collect rainfall from any rooftop surface, although Mecke recommends sloping tin roofs. Generally, 0.6 gallons of water can be harvested from each square foot of roof per inch of rain received.

“For example, if an inch of rain falls upon a 2,000 square foot roof surface, then 1,200 gallons of water can be harvested. If an area receives an average 18 inches of rainfall per year, then as much as 21,600 gallons of water can be harvested from that roof,” he says.

In a typical home collection system, gutters transport the rainfall into a “roof washer,” which collects the trash, debris, and dust contained in the initial water runoff. After the roof washer is full, the rainwater may go through screens or filters before being diverted into a covered collection tank.

These tanks can be as small as a 55-gallon barrel or much larger, depending upon the roof surface area and potential rainfall to be stored in the tank. Generally, the average cost for storage per gallon of water ranges from 40 cents to $1.25 per gallon.

Storage tanks can be painted or decorated as desired. Faucets or gate valves installed at the bottom of the tank allow water to be used on the landscape.

“Covered storage is very important. This significantly reduces the likelihood of trash entering the tank, algae growth, mosquito breeding and infestation, and water losses caused by evaporation,” Mecke says. This is very important since evaporation losses can be extremely high in the southern High Plains area.

Many businesses and homeowners across Texas rely upon rainwater harvesting to meet their entire water needs.

“The Lady Bird Johnson Wildflower Research Center in Austin is probably the best known large- scale (commercial) use of rainwater harvesting in Texas. The center has an entry cistern which holds 12,000 gallons of water and the 43–foot tall observation tower has a 5,000 gallon cistern in the middle of it. These are part of the center’s 60,000 gallon rainwater harvesting system,” Mecke says. Among commercial sites in Central Texas is an Austin veterinary clinic that uses rainwater harvesting to supply all of its water needs.

Menard County Agent Billy Kniffen and wife, Mary, use the roof of their log cabin and a nearby barn to collect about 3,000 gallons of water per inch of rain.

Since their rural home relies solely on rainwater, the Kniffens installed low-flow shower heads and faucets, a low-flow toilet, an on-demand hot water recirculating water system, and have used native/low water use plants in their landscape.

The couple also uses water very sparingly. Their overall average water consumption was 35 gallons per person per day, 2,100 gallons per month, or 25,550 gallons of water per year.

Since the Menard area generally receives 22 inches of rain a year, the Kniffens could collect more than 66,000 gallons of annual rainfall. Their sparse use of water allows them to keep a seven- month supply of water on hand at any given time. They can manage their home on only 8.81 inches of rainfall per year.

Kniffen says he installed his rainwater harvesting system (inside and out) for about $7,000. Using a professional contractor to install the system would have boosted the cost to about $10,000 to $12,000.

Costs of home rainfall harvesting systems can vary from as little as $25 for a homemade tank made from a plastic trash barrel to $10,000 for a system such as Kniffen’s. With costs ranging from $85 to $130, commercial rain barrels are complete with all fittings and a screened top. They are available in various colors, sizes, and shapes.

“The payback time on investment in a rainfall harvesting system depends upon the size and complexity of the system, the use of the water (landscape or potable water use), and whether or not it is installed by a contractor,” says Mecke.

“However, the personal knowledge and satisfaction of saving more valuable drinking water has to be to one of the major benefits of rainfall harvesting projects. In my opinion, that may be more important in the long run than any dollar amount figure,” he says.

Although rainfall harvesting is just one of many water conservation techniques, Mecke says people need to be aware of how they use water in their daily lives and take necessary steps to conserve it at all times.

“Too many generations have grown up thinking that we have an inexpensive, dependable water supply. We turn on the faucet and out it flows without any interruptions. However, water conservation will be an essential way of life for our young people in the future if statewide population increases as expected and water supplies decrease,” he says.

Webmaster's Note: Rainfall harvesting projects in the Lubbock area currently include an inverted roof at Lubbock Medical Gardens, 3821 22nd Street, designed by Raimund McClain and Kristina Yu of the Texas Tech College of Architecture.

Rainfall harvesting has been incorporated into the design of the Louise Hopkins Underwood Center for the Arts, which is currently under construction at 511 Avenue K, in Lubbock.

Other entities, including the Texas A&M University Agricultural Research and Extension Center at Lubbock, are also looking at rainfall harvesting as a method to conserve water at their facilities.

Web posted at 9:09 a.m., Tuesday, March 7, 2006.

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