The Graywater Solution To Our Water Crisis

In my last blog I discussed the difficulties of tapping rainwater for potable household use. A more common and feasible approach to water reuse is graywater systems that recycle waste water from showers, baths, lavatories and washing machines for non-potable purposes such as toilet flushing and lawn sprinkling.

Some ecologically conscious people do this by hand, by collecting shower water in buckets and using it to flush toilets or water gardens. That’s admirable, but labor-intensive and inefficient. Since 2010 the California Plumbing Code has allowed the installation of residential graywater plumbing that enables dedicated conservationists to automatically recycle graywater for non-potable uses.

First, let’s distinguish between graywater and dirtier forms of waste water, which the California Plumbing Code forbids even for non-potable household recycling. (While graywater is not permitted for potable use, plumbing codes err on the side of caution in allowing only recycled graywater that is reasonably safe if ingested accidentally.)

The stuff that flushes down your toilet and into the sewer is referred to as “blackwater.” Although it is technically feasible to purify blackwater all the way to potability – astronauts drink recycled urine, after all – it requires advanced technology. Some jurisdictions also make a distinction between graywater and “darkwater,” which is kitchen waste water that may contain food contaminants, oils and dishwashing detergents. In some cases this water can be used for landscape irrigation, while other jurisdictions ban its use outright.

That leaves graywater from showers, baths, sinks and lavs, and washing machines (within limits). The California Plumbing Code permits graywater recycling from washing machines, as long as the system does not contain water used to wash dirty diapers, materials containing hazardous chemicals and other restrictions.

Even within the restrictions, the potential for water savings from graywater recycling is enormous. Studies have shown that somewhere around 60% of household water use ends up as potentially reusable graywater, amounting to around 25 gallons each day per person. A family of four may produce enough graywater to water more than 2,400 sq. ft. of lawn and garden even in semi-arid Southern California.

If you are building a new home you can design the plumbing to include graywater reuse features, but many existing homes don’t lend themselves to easy graywater retrofits. For instance, if your home is built on a slab foundation, most drain pipes are buried beneath the concrete slab and that would require very expensive work to install a graywater system. If your home is built on a raised foundation, a plumber generally can access fixture drains via a crawl space and make graywater connections. The more fixtures you include in the graywater collection system, the more graywater you will have for landscape watering. If you are building a new home or doing an extensive home remodeling project, you may want to consider including graywater piping in the plan.

As a practical matter, the most common home graywater systems involve diverting washing machine water to landscaping. That’s because most washing machines are located near an outside wall or in a garage, which makes them relatively simple to connect to an outdoor sprinkler system.

When washing machines or fixtures are located on upper floors, it’s possible to design a graywater system that operates strictly by gravity. However, these systems can be very difficult to design and operate effectively. Most graywater systems will require pumping stations along the way.

The upfront costs can be expensive, but that must be weighed against water savings and healthy greenery for years to come. Factor in also that your water rates are likely to keep going up. And if our current drought conditions persist, factor in the likelihood that the lawn and garden that give you so much pleasure will be subject to draconian water restrictions.

Many golf courses and commercial landscapes can survive only by using recycled water. The day is not far in the future when the same will hold true for the flowers and foliage that surround your home.