Is a Passive Greywater System for You?

Simple passive greywater systems use recycled water to irrigate plants and save money.

Passive greywater systems, which use recycled water to irrigate plants, can shave 30% off a household's total water use. Image: Tyler Walter

Americans use more than 7 billion gallons of water a day for landscape irrigation and tending gardens, according the Environmental Protection Agency’s WaterSense program. As much as half of that water goes to waste from evaporation, system leaks, and overwatering. Unfortunately, you’re using—and paying for—fresh drinking water to do all that watering.

Inside the house, the average American family of four generates about 200 gallons of water a day that’s considered greywater, the EPA says. That includes water from bathing, bathroom sinks, and laundry that doen’t include dirty diapers. (Water from the kitchen sink and dishwasher has too much organic material in it to be considered safe for reuse.) It’s water that goes down the drain into the sewer or the septic system. But in the right circumstances, it could be reused for irrigation.

The greywater produced by the typical U.S. household isn’t enough to irrigate an entire yard. But according to a 2006 study by the Water Environment Research Foundation, it would take care of half the irrigation needed for a 2,500-square-foot house on a quarter-acre lot that’s landscaped with drought-resistant plants.

Why use greywater?

There are several reasons to consider installing a greywater system for irrigation. The most obvious is cutting back on your water bills.

“It’s a great way to save water. You’ve already paid for it once and you get to use it again,” says Laura Allen, co-founder of Greywater Action for a Sustainable Water Culture, a non-profit organization that provides education about sustainable water systems and practices.

It’s also worth considering if you live in a place with persistent water restrictions, if you have a septic system that is in danger of failing, or “if you’re excited about products that are good for the environment,” Allen says. 

Greywater restrictions

The biggest obstacles to putting in a greywater system are local regulations—in many parts of the country greywater systems are not allowed due to health concerns. Even in places where they are legal, there are strict limitations on their use because greywater may contain contaminants.

In Arizona, for example, greywater systems can only be used on lots where the water won’t run off on to someone else’s property, and where the groundwater is at least 5 feet below ground level. It can’t be sprayed on landscaping; it has to be used in flood or drip irrigation, and it can’t be used on any plants that produce food, except for citrus and nut trees.

Greywater behavior

Even if greywater systems are allowed in your area, they’re not for everyone. Using a greywater system often requires changing your bath soap, shampoo, and laundry soap to ones that don’t have chemicals that could pollute the groundwater. Plumbing systems that have filters should be closely monitored and the filters changed on a regular basis or they won’t work. 

“There are some behavioral changes that for most people would be something to bear in mind,” says Tom Bruursema, general manager of the wastewater treatment unit program for NSF International, an independent testing organization for food, water, and wastewater. “Bleach and other normal products may not be able to be used to have the system function properly.”

Choosing a greywater system

If you are considering a greywater system, there are a number of options, ranging in both complexity and cost. The simplest systems are the best, says Art Ludwig, an environmental systems designer and author of “Create an Oasis with Greywater.” He lists 20 different options in his book. While most are relatively simple and straightforward, some heavily engineered systems intended to provide water from septic systems can cost $30,000.

One simple, inexpensive system is called “laundry to landscape.” It uses the pump in a washing machine to distribute the greywater outside the house and into a mulch basin—a shallow trench or ditch filled with mulch that serves to keep the soil moist around key plants. The mulch prevents evaporation and acts as a filter to remove and degrade any solids, such as lint from towels.

A skilled do-it-yourselfer can build the system for $100 worth of parts, Ludwig says. Installed professionally, it would run about $500. “Handy people can save the majority of the cost, as labor is the main factor,” he says.

The branched drain is another simple system. Its basic component is a multiple-direction valve that allows the user to choose how to direct the greywater. If the water is from the shower, it can go to irrigation. If the greywater comes from a laundry load of diapers or a load washed with bleach, the valve would be flipped to discharge the greywater into the sewer or septic system.

A skilled do-it-yourselfer with knowledge of plumbing and landscaping could build a branched drain system for $200 to $300 in materials, Allen says. To have a plumber install it, the cost would run $1,000 to $3,000.

How much can you save?

Greywater systems could save you as much as 30% of your total water use, Ludwig says. Savings will vary by local water prices; the main savings are in septic maintenance that’s avoided, and external ecological benefits, such as reducing overall demand for potable water.
Because the average U.S. family spends about $500 a year on its water and sewer bill, savings from a greywater system may total $150. You may also be able to convince your water department to lower your sewer bill because you’re not putting as much water through the system.

Over the years, Allen says she has had various greywater systems in her house, and has gradually become “simpler and simpler. I’ve abandoned all the things that require maintenance. Every year or so, you have to replace the mulch, but if you forget, nothing terrible will happen.”