How graywater systems reduce potable water use
Waste not, want not.
When trying to learn about being green and reusing water, one can feel suffocated by all the terminology. There’s graywater, blackwater, reclaimed water, recycled water, potable water and nonpotable water. Let’s start with defining these terms.
Graywater is water from bathroom sinks, bathtubs, showers and washing machines. Blackwater is from toilets, kitchen sinks and dishwashers. Potable water is synonymous with drinking water and can be consumed with no health risks. Nonpotable water, however, is not safe to drink, but can be used in irrigation and toilet flushing. When nonpotable water is treated, it is then called reclaimed or recycled water depending on the state you live in. In addition to graywater, nonpotable water can come from rainwater and municipally supplied reclaimed water.
Because graywater contains less pathogens and nitrogen than blackwater, it requires a lower level of treatment. “In a typical plumbing drain system, graywater would be sent to the sanitary sewer system,” explains James Paschal, chief technology officer at Aquatherm. “An on-site treatment system will filter and treat the water so it can be used for nonpotable applications.”
Rather than using potable drinking water in a toilet, a graywater treatment system will separate the two streams of water. It collects and stores the graywater, treats it and then sends it out to toilets and irrigation. Purple piping is the industry standard color designating that the water flowing through the pipe is recycled.
Eligible for LEED, NGBS points
Graywater reuse systems, including the purple piping, are addressed in both residential and commercial building codes in IAPMO’s 2012 Uniform Plumbing Code and the 2012 Green Plumbing and Mechanical Code Supplement. Such systems allow for a reduction in potable water consumption and savings on the annual water bill of the building or home.
Many companies make the purple piping used in these systems. Charlotte Pipe & Foundry manufactures ReUze, a purple CTS CPVC pipe used to distribute nonpotable water inside the building and is installed the same way traditional piping is. Uponor’s purple pipe is made from flexible PEX-a tubing, which carries water (both reclaimed and potable) throughout the building. Aquatherm’s Lilac pipe is similar to its other pipes using PP-R construction and heat-fused connections.
“The actual installation process is the same as it would be for other plumbing systems,” Paschal says, “but the system design must ensure the recycled water piping is not connected to the potable water piping at any point. There are also marking requirements for the pipe which clearly identify it as being for recycled/reclaimed and nonpotable water.”
Jayson Drake, director of plumbing and fire safety for Uponor North America, believes the plumbing market in general is increasingly leaning toward using nonmetallic, cross-linked polyethylene as the tubing of choice “due to its reliability and ease of installation. The fittings used in these plumbing systems also are trending to nonmetallic solutions, such as engineered polymer.”
Graywater reuse systems are a factor in both LEED and National Green Building Standard. LEED v4 has three prerequisites and 12 available points for water efficiency. Greg Nahrgang, new product development manager for Charlotte Pipe, says the categories can be broken down into indoor use, outdoor water use reduction, metering and cooling tower water use. Receiving all 12 points makes up about 30% of the 40 points required to receive LEED certification.
Drake adds when toilets are flushed with graywater they can qualify for four NGBS points and irrigating with graywater can qualify for 10 points (section 802.1). “Although these points might not seem to be significant, they do contribute to the total number and they are driving increasing acceptance of, and adoption for, graywater systems.”
However, installing a reuse system involves additional requirements, including system maintenance, testing and inspection, component marking/identification, maintaining separation of the system from the potable water system, operation and diversion of water to and from the sanitary system, system sizing and installation location, Paschal explains.
New construction vs. retrofit
Graywater reuse systems can be installed in new construction as well as retrofit projects. Most in the industry agree that installation of a system done during new construction is fairly simple, while retrofitting is much more complicated. Cost and ease also vary considerably on a case-by-case basis.
Nahrgang explains these systems can be anything from a simple rain barrel under a downspout used for irrigation, to a container with a diverter on it running the water to a toilet, to a 62,000-gal. tank buried underground that sends water throughout the building to all the toilets, urinals and cooling tower makeup water.
“If you have something really simple,” Nahrgang says, “such as catching rainwater and using it for irrigation, you could get all the materials and install it yourself for probably $50. On the other hand, large commercial projects using nonpotable water systems can spend several hundred thousand dollars on them.”
Douglas Kirk, director of IAPMO’s green plumbing curriculum, adds: “One or two fixtures located on an exterior wall is fairly simple. A full retrofit, accessing all fixtures which may discharge to graywater, will range from fairly expensive to impossible.”
Paschal says graywater typically is not separated from other waste. “Making this physical separation in the piping will require getting access behind walls and in floors at every fixture where the graywater is being recovered,” he explains. “In addition to gaining access and diverting the piping, an entirely separate drain line needs to be run from each of these graywater fixtures back to the recycling treatment system.”
In these situations, Drake advises building owners and homeowners to consult with a local professional plumbing installer for a realistic cost comparison.
Drought, utility rate increases
Graywater reuse systems have come a long way. Many in the industry say it is definitely a growing market, albeit a slow one. Nahrgang believes a trigger, such as a severe drought or a sweeping government mandate, will cause these systems to be implemented more quickly.
Kirk agrees potential exists for the market to grow, especially in new construction — the most common use will be for irrigation. “Some property owners spend thousands or tens of thousands of dollars on landscaping,” he says. “With such an investment, when utilities call a halt to using potable water for irrigation, it seems graywater may be their only alternative.”
He adds that because water and sewer utility rates are increasing faster than almost any other utility, the use of potable water to flush toilets and irrigate landscape will have to be reconsidered.
“The other big trigger for this industry will be government involvement,” Nahrgang comments. “For example, in the Bay area of San Francisco, the municipality has stepped in and said new structures over a certain square footage or meeting a certain profile will be piped with nonpotable water piping. It doesn’t make sense to use drinking water to flush our waste down the toilets or to water our yard. We have a fixed amount of water; we have to use it wisely.”
Drake says the market for graywater systems will be greater for new buildings than for remodels because of the ease in which a system can be installed and achieve green standard points.
“As water scarcity issues continue to expand, we certainly expect demand for PEX-based graywater systems to increase accordingly,” he adds.
Paschal believes the recycling of water, rainwater catchment systems and lower water-consumption plumbing fixtures are becoming the norm across the country.
“The next logical step will be to treat the water to the level of being used in the potable system,” he explains. “The technology for this exists today, but the safeguards needed in terms of proper system operation and maintenance make it difficult to safely implement.”