June 1, 2007

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COLLEGE STATION – When the weather turns dry, Texans may start thinking about the best ways to avoid high water bills and still maintain their landscaping. Gray water may be one option, said Dr. Bruce Lesikar, Texas Cooperative Extension agricultural engineer.

Gray water is the water that has passed through showers, sinks, bathtubs or washing machines, Lesikar said. It makes up about half of the water used in the home and normally passes into onsite wastewater treatment systems or city sewer systems.

"The typical resident will have about 30 gallons per person per day," he said.

"Gray water is a source (of water) that's already paid for, and you can use it in your landscape," he added.

It is different from black water that comes from the toilet or kitchen sink. Black water has the potential to have many solids and therefore cannot be used on landscapes without treatment, he said.

Gray water is not without risk, though.

"It does come into contact with the human body so there is a risk for having organic matter as well as pathogens," Lesikar said. "So it needs to be used safely and wisely."

Also, gray water may contain high concentrations of sodium and phosphorus from soaps, detergents and cleaning products. If not leached out, these can build up, harming soil health, he said.

State regulations affect how gray water systems may be installed and used, Lesikar said. A typical gray water system consists of a diversion valve to direct gray water to the reuse system, a tank to separate solids, an effluent screen to trap solids before they leave the tank, an overflow pipe with two black-water valves going to the onsite wastewater treatment system or municipal sewer, and a distribution system delivering gray water to the plants. The pipe for distributing the water must be purple to designate that it is reclaimed wastewater.

A gray-water system must be used to avoid ponding or build-up of water on the ground surface, he said. Ponding may cause nutrients and salts to build up in one place in the yard, or it may attract nuisances like insects.

Plus, if pets play or roll in wet areas, they could bring wastewater back into the house.

"Because there is the potential risk in ponded water, pets may be exposed to pathogens," he said.

Typically, gray-water systems that are whole-house systems are completed at the time the house are built.

"If you are planning on a gray-water system, you have to start by planning early," he said. "Houses that are on blocks or above the ground do have the ability to be re-plumbed to separate gray water for use. For houses that are on slabs, it is more difficult to separate the sources once the house is built."

If washing machines or other sources are on exterior walls, however, homeowners can plumb through the wall and access that water, he said. However, the gray-water tank must be able to overflow through two back water valves to the onsite wastewater treatment system or municipal sewer to be in compliance with state regulations.

Gray-water systems may be used on all soil types. However, sites with heavy clays will not easily accept water and will tend to be wet during winter months, Lesikar said.

In that case, have a diversion valve at the beginning of the system. This allows the gray water to be diverted to either onsite wastewater treatment systems or city sewers if needed or if conducting maintenance on the system.

Like most everything else, gray-water systems do need routine maintenance, and the solids will have to be removed from the tank periodically, he said.

Wear gloves when working on systems to protect against pathogens, Lesikar cautioned. The diversion valve, though not required by state regulations, will allow water to be diverted into black-water systems and reduce exposure to pathogens.

Tanks and rigid purple pipe may be purchased at plumbing supply stores, he said. However, flexible pipe may have to be painted purple, he said.