Building Codes Are Last Obstacle to Wider Use of Graywater in Homes


Using graywater to flush water is a big water saver. Modern Design + Construction spec’d this purple pipe system from Harvest2o in a house in Santa Fe. The 2012 UPC and UMC codes that permit this stipulate that the water be brought back into the house.

Today, the technology and know-how exists to take graywater from washing machines and showers—as well as rainwater collected from roofs—and use that water to flush toilets and irrigate landscapes. That same water can be brought back into the house, treated, and used yet again. It makes a lot of sense and saves a lot of water, so why isn’t it happening, or even mandated, everywhere?purple_pipe_washer

“All water reuse scenarios are doable, and most of them are covered by the current code,” says Doug Pushard, founder of HarvestH2o and a designer of residential water management systems. “However, there are some holes—the codes have not been integrated. The rainwater code was driven by the American Rainwater Catchment Systems Association, and the graywater code came from states doing it and publishing best practices.” (Learn about HarvestH2o’s Rainwater calculator here.)

Mixed Messages
An example of where adoption gets tricky is mixing graywater and rainwater in the same tank. “This practice is not yet covered in the codes,” Pushard notes. “The purification is almost identical, but I have a feeling when I go to do my first one this year in Santa Fe, they will not allow the mixing of these waters. I will have to have two tanks and two filtration systems.”

That adds up to extra costs for homeowners, he explains, and slower market penetration.
Builder Kim Shanahan, executive officer of the Santa Fe Area Home Builders Association, is at the forefront of water conservation efforts in the water-conscious city. Because Santa Fe adopted certain codes, the municipality is poised to take advantage of water-saving reuse. “We are going to be allowed to bring water back into the house,” he says. “We adopted 2012 UPC and UMC Building Codes, as well as some chapters of the code that the State of New Mexico hasn’t even adopted.”


HarvestH2o designed this purple pipe system for a house built by Modern Design + Construction to use graywater for clothes washing. With an average U.S. household doing about 400 laundry loads a year, this is a big water savings.

The upshot is that the municipality can bring water back into the house and reuse that water for toilet flushing and washing. “It’s not unique to Santa Fe,” Shanahan reminds. “Anyone using 2012 UPC and UMC Codes in their entirety can do this.”

The code is quite strict. It stipulates, for example, that the water being brought back in the house, even for use in toilets, be “potable,” ostensibly to protect pets or kids who happen to dip into that toilet water.

Shanahan says even this high bar can be reached, however: “We know we can treat water that has come back in the house to this higher standard than the required level, and we have the filtration and UV technology to do this. It is the future for homes: net zero energy, net zero water (see “Double Zero”).”

Burdens of Proof
Right now, Shanahan is battling codes and, therefore, costs. “It could be expensive to convince an engineer and building code officials that a water reuse system is foolproof,” he says. “You need a filtration and UV system and have to have a failsafe delivery system, and a backflow preventer.” Without all of this codified, it could be challenging for building officials to approve on a project-by-project basis.

While codes catch up to what innovative designers and builders can do, Pushard thinks it’s best to use rainwater in the house as it is the highest quality. “Oftentimes, rainwater is better quality than the source water for most municipal water companies,” he notes. “It doesn’t take much treatment to get to flushing quality, nor to potable quality.”

The International Code Council is currently working on a standard draft that will include both non-potable and potable rainwater, which should be out later this year.

Water Rights Complexities
The issue of downstream water rights has hampered code adoption in many areas.
Colorado is a well-publicized example of the tricky business of water reuse. Because of water compacts with downstream users, the state outlaws capturing roof water. But in reality, simply using water twice or three times before letting it go downstream shouldn’t reduce the amount of downstream water and in fact could actually increase it while making it more manageable.

“Capturing rainwater reduces stormwater,” explains Pushard. “By using it inside actually increases the amount of water going into the sewer system but on a slower, more manageable basis. For cities, with or without combined sewer/stormwater systems, this is an easy, less-costly approach, which can reduce or eliminate the need for expensive system-wide upgrades.”

Almost everyone is downstream of someone else upstream,” Pushard points out. “The loop is just getting smaller.”

“The plumbing code chapters we’ve adopted address roofwater and runoff, which opens things up, especially in West with limited water resources,” says Shanahan. “Water is a limit to growth, and with more people coming here and fewer resources, the only solution is to wring more water out of the available building lots.”

Pushard thinks individual water treatment “plants” in homes are the answer to a water-smart future: “The projects that get the most press coverage are the big whole system projects. That’s one approach. Another is house-by-house, neighbor-by-neighbor, community-by-community, until it is just part of the invisible infrastructure.

“Few people had indoor bathrooms 100 years ago,” he adds. “A hundred years from now, we will all be harvesting water and sending it back into the system, both potable and non-potable. It just makes good sense.”

Water-Saving Case Study: KB Home 

National homebuilder KB Home has been challenging the status quo with its Double ZeroHouse projects.

Several demonstration homes, located in drought-prone central California, are designed not only to achieve net-zero energy, but to demonstrate water conservation, both inside and outside the home. Double ZeroHouse 2.0 was built in Lancaster, California. More recently, Double ZeroHouse 3.0 was completed in KB Home’s Fiora at Blackstone community in El Dorado Hills.

Both homes feature Nexus eWater graywater treatment systems. These combine the eWater Collector, the NEXtreater, which treats graywater to near-potable standards, and the NEXservoir, which stores treated graywater. The Double ZeroHouse in Lancaster uses treated graywater to irrigate landscaping, saving up to 40,000 gallons a year. The El Dorado Hills project uses the graywater to flush toilets and also features the NEXheater, which uses a heat pump to extract heat from graywater and uses it to heat incoming potable water.

This is close to perfect, but according to Shanahan, it is important for the water to not just be near potable, but potable to ensure pets and children who might come in contact with toilet water don’t get sick. It will probably also be stipulated in the upcoming ICC codes out later this year.

Simple Does It
While others eager for more sophisticated graywater/rainwater storage and filtration systems duke it out in the codes arena, builders can start with a simple, cost-effective landscape irrigation system.


Typically a laundry to landscape system works like this: the washing machine is connected to a 3-way valve. Water can go to the graywater system, or sewer/septic. The graywater valve is sent through PVC piping, which delivers it to one or more outlets in the landscape, where it percolates through a mulch shield, which keeps the outlet from clogging with debris.

Bill Roth, president of Modern Design + Construction in Santa Fe., N.M., has been working on graywater systems for 10 years. “We don’t do capture systems, just distribution systems. You take the water out of the house and to various locations. These systems aren’t bombproof, but they don’t have any moving parts, and you aren’t treating or storing it.”
In one application, Roth collected the water from all the fixtures of a home, and ran it via 2-inch pipe to two distribution areas (small leach fields) in the yard. He used the calculations provided by the 2012 plumbing codes for minimum side yard capture area.

Roth points out that the technology needed for graywater use is already part of the builder parlance. “It’s taking PVC pipe, dual plumbing fixtures, backflow valves, a manhole, and a bit of engineering,” he says.

Selling clients on graywater is straightforward. “It’s a case of sitting down with a client and introducing the concept of a passive gray system early in the game,” he says. “In a lot of cases, they are interested because of the low cost.” He estimates a system may add $800 to $1,000 to the price of a 1,500-square-foot house: “It’s a lot easier sell than rainwater catchment, and it’s a lot of water … a lot of water.”

Interested in more stories about water conservation? Check out this article, WERS: A New Tool for Water Conservation.


Photo by jemasmith