November 13th, 2007

How-To Tuesday: Graywater Systems

Posted by Jason Pelletier, Low Impact Living

We get many requests here at Low Impact Living about all sorts of green building and living topics. One of the most popular by far is how to install graywater systems. We’ve held off on writing about it, because it’s a pretty tough topic - in many parts of the country, government permitting agencies make it VERY difficult to put one in, so there’s not a huge installed base to review out there. But, the crescendo keeps rising, so we’ll do our best to provide you with some relevant tips!

What is Graywater?

First off, it might be helpful to define what exactly graywater (or greywater, in some circles) is. At its most basic it is any wastewater that comes out of your house that doesn’t contain human or organic wastes. In practice, it is the water that comes from your tubs, showers, non-kitchen sinks and laundry machine. The rest, from your toilets, dishwasher and kitchen sinks, is called black water (no relation to that infamous Iraq contractor!).

A graywater recycling system takes this water, filters it, passes it through a short-term storage tank and then either routes it to irrigate plants in your yard or to the subsurface below your yard where it eventually flows down to the groundwater table. Simple systems are often the DIY projects of industrious homeowners - a separate drain line installed below the house for graywater fixtures connected to a sand filter and on to conduits that convey it to lucky trees or plants (we don’t recommend these due to the permitting issues, but more power to you if you’ve been able to set one up!). Some landscape and engineering firms can build similar versions that have all of the necessary checks and balances, but are obviously more expensive. Perhaps the most exciting developments are the increasing numbers of companies coming out with prepackaged units that make maintenance and installation much easier (more on these later).

What Are The Benefits of Graywater Systems?

The benefits of graywater systems are as follows:

– Reduced use of potable water for irrigation. This can be a critical benefit in drought-prone areas, and can save you a lot of money in areas with high water rates. In most areas of the country, a graywater system could provide all of your outdoor landscaping water and save you $50 - $200 / year in water charges.

– Reduced sewage discharge. This too is a major benefit - less sewage means less demand for treatment plants down the pipe. And in certain areas you can get an allowance for such a system that allows you to pay less in sewage fees each year. Sewage fees are often equivalent to water rates per gallon, so you save double with a graywater system.

– Healthy plants. Graywater is relatively high in nitrogen and phosphorous (from detergents). These are two of the three main components of fertilizers, so for the right kinds of plants graywater can be a major benefit. Citrus trees are a good example. Be careful here, though - some types of plants don’t tolerate high levels of fertilizer and can actually be harmed by graywater discharges. Many Southern California native plants fall into this category. They like acid, dude, and graywater is very alkaline! So, check with your local landscaping contractor or read up on your plants before you dive in.

Graywater Options

There are many possible graywater configurations, but we’ll review two of the main types here.

First are the custom solutions - those designed and installed by either a homeowner or a landscape / engineering design firm. You would typically have the following components in such a system (see diagram at right, courtesy of www.greywater.com):

– A separate waste plumbing system leading from sinks, showers, tubs and clotheswasher.
– A bypass valve, which can be used to reroute graywater into the standard septic or sewage system if necessary.
– A surge tank, which stores water temporarily while it cools, and also acts as a buffer for high flows from clotheswashers and showers.
– A pump, to pump the water into the discharge system.
– A filter, which screens out sediment and particles.
– A check valve that ensure water can’t back up into the system from the irrigation pipes.
– A subsurface drip irrigation or perforated piping system, or a drywell to convey the water underground.

Second are a newer breed of prepackaged systems. These systems combine many of the elements into one piece - you still have to install the drain pipes in the house and the irrigation lines in the yard, but all of the other components come in one unit. One good example of such a system is the ReWater System , made by ReWater Systems in Southern California. They have installed systems throughout the Southwest. Another newer entrant is Perpetual Water, which makes a range of units from a version that treats just your clotheswasher water to a whole-house system. Although new to the US, their systems have been used for several years in Australia. Still another interesting option is the Brac Systems graywater recyling option. It can be installed inside, and the output can be used in toilets or for irrigation (depending on local plumbing codes). One last example is Clivus Multrum Incorporated. They’re located in Massachusetts and have made graywater systems for years (and also make composting toilets if you REALLY want to cut your water use and waste production!).

Important things to consider

We love graywater systems, and hope to install one in our home at some point. However, this is definitely a project that takes planning and perseverence to pull off. Here are some of the challenges you might encounter:

– Permitting. Many local health and safety agencies are very uncomfortable with graywater systems, fearing that they will lead to drinking water contamination and other health hazards. They often make it difficult or impossible to secure the necessary permits, even in areas where it is technically legal (such as Los Angeles!). Before starting your project, make sure you check with the local powers that be. It would be a waste (no pun intended!) if you had to pull out that beautiful new system when you go to sell your house.

– Subsurface discharge. While safer than blackwater, graywater still contains some bacteria and other pollutants. In most places the only legal way to plumb a system is via subsurface pipes or drip irrigation fittings. Some DIYers, though, will lay the pipes on the surface and cover them with mulch - think very carefully about whether this is safe in your yard before you do this!

– Safety Marking. Make sure you mark all pipes, both in the house and yard, with the appropriate caution and graywater labeling.

– Detergents. Use liquid and relatively mild (or biodegradable) detergents. These will ensure that your plants don’t get nourished to death. And, don’t use chlorine bleach.

– Make sure you have an air gap. MAKE SURE you consult a plumber if you are installing a graywater and standard irrigation system in parallel. You need to build in an air gap between the graywater system and any fresh water plumbing, lest a backup / plug force graywater up into your freshwater system. That can be a very bad result indeed. We recommend keeping the two systems completely separate.

For more info on graywater systems, you might want to check out the Oasis Design website. It is truly a treasure trove of information for anyone from the homeowner to the true professional. And here are two documents (Doc A and Doc B) from the State of California that provide helpful information on sizing and locating graywater systems. If you’re really serious, think about investing in one of these great books on graywater systems.

We hope you’ve found this piece useful - please share any of your success stories with us so that we can help other learn from your successes. Send me an email at info@lowimpactliving.com if you have any great projects to report!