Graywater Systems

Graywater Systems in Texas


Graywater systems: Approximately 40% of household water use in conventional systems is for toilets. The remaining 60% can be run through a graywater system, significantly reducing the demand on a septic tank. This can prolong the life of the blackwater septic system and lateral field. The system that was presented disperses the graywater underground where it is used to water crops such as fruit trees (no root crops that would have direct contact with the graywater!) rather than recycling it for household use such as flushing toilets. Reusing graywater is more challenging because it involves possible human contact with the water, therefore it must be treated more aggressively due to possible fecal contamination.

A filter on the washing machine is important to prevent clogging of graywater system pipes from lint.

A small septic tank is necessary to meet codes in most areas. The small size helps keep the graywater from becoming anaerobic which would result in unpleasant odors. This holding tank allows solids to settle out, and fats to rise. Then water is run through a filter tank of clean gravel before being pumped to the underground distribution pipes. The pressurized system is essential to distribute the water evenly through the pipes, resulting in even watering of the crops. For the underground tanks, plastic is best because it doesn’t leak. Be sure to fill tanks with water immediately upon placing them in the ground, or they may float out!

Two-layer  underground pipes are the unique part of this design. Plastic irrigation tubing with 1/8″ holes is run through perforated plastic drain pipe, 1″ deep, the shallow depth can be used year round if insulated with hay on the ground above the pipe. The air space between the inner pipe and drain pipe helps to insulate the system. Also, the air space prevents roots from growing into and clogging the inner pipe. If the inner pipes ever do need replaced due to clogging, new inner pipes can be fished through the outer pipes easily. The length of the system and the hole spacing depends on the soil type: for a low use household in sandy loam soil, a 50′ system with 10″ hole spacing works. Less permeable soil would require longer pipes and wider hole spacing.

Removing the graywater from the regular septic system has no adverse effect on the septic. The life expectancy of the septic system is based on accumulated solids and bonding of heavy metals.

Bleach should be avoided in drains, as it harms bacteria. Also, use biodegradable cleaning products, and avoid “antibacterial” dish detergents.

Graywater is a fantastic way to provide some water for thirsty plants. The good news is that it is legal in San Antonio. Roderick Sanchez, Director of the City of San Antonio Planning and Development Services Department provided an interpretation of the city rules governing residential gray water dated April 20, 2009. I’ve included a link to a pdf of the interpretation, but for convenience have transcribed the document below: