Graywater

Published in the Sun October 16, 2011

It breaks my heart to see the trees dying.  Trees define a temperate climate; there are no majestic trees in the desert.  Golden brown grass has a certain stoic beauty because we know that when at last it rains the grass will turn green again.  But when hundred year old trees die, they will not be restored by a little shower.

The heat may have let up, and we have even had a bit of rain, but it is unlikely that the extraordinary drought is over.  Did you know that nationwide, 50 to 70% of municipal water is used to irrigate home landscapes?  In Georgetown and Round Rock, that means that water is imported from Stillhouse Hollow, treated to be safe enough to drink, pumped to our houses using electricity, and then thrown on the grass.  What if this is a multi-year dry spell?  Are there ways that an individual could use water more effectively?  Could we still have trees?

People are starting to talk about graywater.  Graywater is water that has already been used in a home’s washing machine, showers and tubs, and bathroom sinks.  It is called graywater because it is not as contaminated as blackwater, which has been flushed down the toilet.  Water from the kitchen sink and dishwasher is also considered blackwater because of the large amount of food waste that may be present.  In some areas where drought is a way of life, graywater is used to flush toilets, but that requires some very sophisticated plumbing.  The most common use of graywater is to irrigate plants.

Paolo Pinto directed on-site sewage facility inspections for the Williamson County Health Department for 18 years, so he knows quite a bit about dirty water.  He has been using graywater on his trees and vegetable garden since his house was built in 1986.  Paolo has a large lot in the Chisholm Trail Utility District, which has been under severe watering restrictions all summer.  Although most of his neighborhood is wooded with native trees, the elms are wilting, and the live oaks don’t look so good either.  All is not lost though, because there is one factor working in favor of the trees:  Paolo’s graywater system.

Paolo’s shower and washing machine do not drain into his septic system.  Instead, they drain into a 50 gallon tank buried in his backyard, and from there by gravity into a hose that he can move from tree to tree as needed.  An eight minute shower uses about 20 gallons of water.  An average top-loading washing machine uses 41 gallons of water per load.  A bathroom faucet produces about 2 gallons per minute.  Excluding the blackwater going down the toilet and kitchen sink, an average American produces about 40 to 50 gallons of graywater every day.  An established tree needs approximately ten gallons of water per inch of trunk diameter every week, so if Paolo generates 50 gallons of graywater a day, he could water a different 5 inch diameter tree each day of the week.

Paolo is quick to point out that his graywater system would not comply with current state laws if it were being built today.  One new requirement is that a system must allow 100% of the graywater to be diverted into the sewer or septic system if necessary.  This is a very logical requirement.  If the ground is soggy from heavy rains, you would want to be able to turn off graywater irrigation.  Or what if there is a baby in the house and dirty diapers are regularly being washed?  Nobody wants diaper water going onto the lawn.

Another state regulation is that the graywater must not be sprayed and must not be allowed to pool or run into a neighbor’s yard, the street, or a natural body of water.  Care must be taken to avoid creating breeding habitat for mosquitoes.  The plumbing that carries graywater must be clearly distinguished as non-potable water, usually by making the pipes purple and posting signs.

Graywater does not adapt well to soaker hoses or drip irrigation because it has a lot of particles and lint that rapidly clog the openings.  Graywater should not be stored in a tank for more than 24 hours, because it contains soap, bits of food, and bacteria, so if it sits around it will stagnate into blackwater and it will stink.

The most effective (and lowest maintenance) graywater systems disperse the water underground as soon as it is generated into a mini drain field where trees are planted.  An anonymous city inspector told me that he has had an underground graywater system irrigating a row of peach trees for years and they look fantastic, even with no additional water this summer.  He does have to be careful about what kind of laundry soap he uses.  Most powdered laundry detergents are high in sodium, which can be harmful to plants.  Borax can also kill plants in even small quantities.  Once his wife got enthusiastic with bleach in the white loads and wiped out a big area of grass.  He also told me that currently there are no City of Georgetown regulations about graywater systems.  As long as the neighbors aren’t disturbed, the code enforcers won’t concern themselves with your laundry water.  Residential codes for graywater may be adopted in the future, but we don’t have them yet.

A graywater system can be a useful way to conserve water, but it is more complicated to install than it sounds, and there is a lot that can go wrong.  Before installing a system, figure out how much graywater your household would produce and how you would use it.  Consult with a plumber.  And don’t feel guilty if it just sounds like too much trouble.  Even if you don’t take advantage of your graywater, the city is already recycling it.  Treated effluent (cleaned up sewage) is used to irrigate the local golf courses.

A useful internet resource for graywater systems is Oasis Design, a California company that has been designing sustainable water and wastewater systems for many years.