How to Re-Use It: Understanding graywater code provisions
How new is new? Or perhaps the question should be: When is something not new anymore? Graywater provisions first appeared in the plumbing codes in 2012, but as we head into the 2015 code cycle, many still do not fully understand graywater systems. This could be largely due to the tendency we humans have to not really invest in something until it has a direct impact on us. Thus, many inspectors and installers tend to not learn about new installations, such as graywater systems, until they begin having to utilize them. It is not a criticism, it’s just human nature. Personally, I never bothered to learn how to change diapers until my son was born, at which point I had to become an expert fairly quickly. Now that the utilization of graywater is spreading to new areas, the inspectors and installers responsible for their proper installation are now a growing group. These “new” systems aren’t necessarily new to everyone, but they are “new” to them. With that said, we will explore some of the basic, introductory concepts and provisions governing these systems.
Chapter 16 of the Uniform Plumbing Code and Chapter 13 of the International Plumbing Code focus on the provisions for alternate water sources for non-potable applications for graywater, reclaimed water and on-site treated non-potable water systems. Provisions for rainwater systems are covered in Chapter 17 of the UPC.
The demand for freshwater conservation around the world is growing while supplies are dwindling, and the cost of producing potable water is increasing. Alternative water sources are a viable means of lessening the demand for potable water in applications where drinking water standards are not required. It is just as important to develop alternate water sources as it is to develop alternate sources of energy. These provisions are a move toward this conservation effort and will ensure the safe use of alternate water sources.
With regards to system design, the UPCrequires the person designing alternate water source systems to be qualified and competent to perform the work. Although section 1601.2 restricts the design of alternate water source systems to those registered or licensed to perform plumbing work, the 2012 Green Plumbing and Mechanical Code Supplement has broadened the eligibility of designers to include those with competency as required by the authority having jurisdiction. For example, most jurisdictions will allow landscape architects to design the downstream side of the graywater system (typically beyond two feet outside the building after alterations to the existing plumbing system). They have a thorough understanding of soil types, root zones of specific plants and erosion control, and are one of the professional categories to become Storm Water Pollution Prevention Plan developers and practitioners. This type of expertise is required to prevent the potential hazards associated with graywater ponding and runoff.
As with anything, there are exceptions. Some of these exceptions deal with rainwater catchment systems, which are systems unto themselves and covered separately from basic graywater systems. For some smaller graywater systems, a person registered or licensed for plumbing work is not required for installation. Many graywater systems are very simple and are often based on gravity drainage with no tanks or pumps. Even the small pumped and filtered manufactured-type graywater systems are very simple to install, usually taking only a few hours. If the system has larger volumes of water, or is from commercial buildings, a licensed person is required to design the system.
A common use for graywater is subsurface irrigation, where captured water is reused for watering vegetation. The codes identify three types of graywater systems:
- Subsurface irrigation, where drip emitters are buried two inches below finished grade;
- Subsoil irrigation, where large-diameter pipe is buried in deep trenches to permit deep root irrigation and rapid dispersal of graywater; and
- Mulch basin, where graywater discharges into a mulch-filled basin to irrigate deep-rooted plants.
There have been many studies regarding the amount of coliform bacteria, nitrogen, biochemical oxygen demand, phosphorus, pharmaceuticals and endocrine suppressors that are present in graywater. To limit these contaminants, graywater sources are restricted to only bathtubs, showers, lavatories, clothes washers and laundry tubs (see definition for graywater in UPCSection 209.0 and IPCSection 202.0) and may only discharge to subsurface or subsoil irrigation systems, or a mulch basin. Graywater systems are not permitted for any above-ground irrigation that may allow any potential for human aspiration, nor for many food crops. These restrictions reduce the risk for direct human contact with graywater, while promoting beneficial use from this source of water.
In multi-unit and/or multi-story buildings where graywater requires suds relief for water used in laundries, care should be taken to assure the suds relief is accomplished before discharging to the irrigation system.
When California adopted emergency provisions for graywater during the 2009 code cycle, the laundry was allowed to be installed without a permit as long as the system did not alter the existing DWV system. Typically, systems are installed without a trap and use a vacuum breaker to facilitate flow. The trap prevents pests and insects from entering the building through the irrigation piping. Also, note that there is no air break for the washer when the valve diverts graywater to the irrigation field. The intent for the air break is to prevent sewage (black water) from entering into the washer. If the irrigation line backs up, the only material to enter the washer is material that was discharged from the washer to begin with. Many similar systems use a check valve to prevent backups through the irrigation piping. Since there is grit and dirt being discharged, check valves would need frequent maintenance and to be installed with unions. This system is non-compliant with the 2012 UPC, where Section 1602.2.3 requires the discharge of graywater to occur downstream of the fixture trap and vent as shown in Figure 1602.2.1a.
Using a filter in this system is not recommended since the pressure drop across the filter would strain the pump, leading to premature failure. The system uses the pump from the laundry machine to discharge the graywater to the landscape area under pressure and allows for the use of smaller piping.
Another alternative is the dual standpipe system. One drain is for the irrigation line and the other is connected to the sewer. In time of infrequent use (seasonal irrigation) a “jim cap” or wing nut test plug may be used to cap the unused drain to prevent the introduction of sewer gas into the building.
Since graywater is non-potable, it is important that it does not contact the edible portion of any food plant so as to avoid accidental ingestion of graywater via a food source. This includes root crops (foods that grow underground) such as carrots, beets, radishes and turnips, and any food crop that comes in direct contact with the soil such as pumpkins, melons, squash, cucumbers and potatoes. Above-ground edible portions of food plants that do not contact the soil, like fruit, corn, or tomatoes, are permitted to be irrigated with subsurface graywater and are safe to eat.
Although we have only begun to delve into all of the concepts and code requirements governing graywater systems — and have not even mentioned their use for flushing water closets and urinals — it is important to note that these systems are intended to be designed and installed so as to strike a balance between water conservation, and health and safety. As these systems become more widespread and become “new” to more people, a proper understanding of the codes regulating these systems is vital.