Conserving with gray water
Alternatives are good: Saving the world safely with gray water
When I first found out I was going to be having a boy, my initial plan was to raise a power-hitting major-league first baseman. It was a sound strategy at the time. First base has a relatively low risk of injury and the potential of a long career and several big-money contracts. Sounds like a great retirement plan if you raise your perennial all-star with great family values, right? Sadly, at the age of six, I can already tell you professional sports are not in my son’s future. Despite having the size and some ability, my son tends toward the arts, and is too nice and passive to really be a great athlete. He loves being on a team, but it is hard to be a standout athlete when he stays 20 ft. away from the soccer ball at all times.
Since he was very small, he has always enjoyed art and creating things, which is good since art is typically not a full-contact activity. His media of choice? Recyclables. There is a weekly battle in the house as he tries to hoard all of the plastic bottles and boxes so he can turn them into a jet pack, light saber, a water feature featuring multicolored water or a superhero costume. So, with his love of reusing materials, his creative nature and affinity toward superheroes, I have no doubt he would fully appreciate the creative product and design innovations that have made reusing gray water a feasible sustainability practice that helps save the world’s water supply. At least he would if he were older … and interested in the plumbing industry.
If he were interested in gray water systems, I would have to start by telling him the discussion starts with section 1502 of the Uniform Plumbing Code and that, although gray water systems can greatly reduce the use of potable water in applications that really don’t need it, there are some health and safety issues to take into consideration when you plan for the system. This section identifies three types of gray water 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 gray water; and
- Mulch basin where gray water 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 gray water. To limit these contaminants, gray water sources are restricted to only bathtubs, showers, lavatories, clothes washers and laundry tubs (see definition for Gray Water in Section 209.0 and Figure A); and may only discharge to subsurface or subsoil irrigation systems, or a mulch basin. Gray water 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 gray water, while promoting beneficial use from this source of water.
Figure B is an example of a clothes washer discharging to a subsurface irrigation system. In multiunit/multistory buildings where gray water requires suds relief, care should be taken to assure that the suds relief is accomplished before discharging to the irrigation system.
When California adopted emergency provisions for gray water 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. Figure C shows the most common system being installed and taught by gray water advocates.
Typically, systems are installed without a trap and use a vacuum breaker to facilitate flow (depicted on the left hand side of the drawing). The trap prevents pests and insects from entering the building through the irrigation piping. Also, note there is no air break for the washer when the valve diverts gray water 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 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 be installed with unions. This system is non-compliant with Section 1502.2.2, which requires the discharge of gray water to occur downstream of the fixture trap and vent as shown in Figure B.
Using a filter in this system is not recommended, because 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 gray water to the landscape area under pressure and allows for the use of smaller piping.
Another alternative is the dual standpipe system (see Figure D). 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 gray water is nonpotable, it is important that it does not contact the edible portion of any food plant so as to avoid accidental ingestion of gray water 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 gray water and are safe to eat.
Due to the organic matter and nutrients typically found in untreated gray water, storage longer than one day is undesirable and unhealthy. The nutrients break down, using oxygen and causing malodorous emissions. Bacteria can also breed in the tank, decreasing the quality of the gray water and increasing the potential for unhealthy constituents. However, once gray water has been distributed into the ground, nutrients are taken up by plants and the soil bacteria break down other constituents, preventing any development of odor or health hazards.
Pooling and runoff should not occur in gray water systems, as both will cause a potential for the gray water leaving the property and entering a storm drain. The pooling of gray water could also provide a mosquito breeding habitat.
Gray water diverter valves are needed to divert the gray water to the sanitary drainage when either the gray water is not needed (e.g. plant dormancy, rainy periods or winter season), or when the gray water is hazardous, containing unhealthy contaminants (e.g. hair dye, pesticides, herbicides, cleaning chemicals, solvents, toxins, medications, etc). Where valves are not physically accessible, a simple electronic actuator can be included to allow for a switch inside the dwelling to control the valve. See Figure Bfor a proper placement of a three-way diverter valve.
Note: There are no known diverter valves specifically labeled for “gray water” in the U.S. market. Typically, valves manufactured for the pool and spa industry are used. They are not manufactured in ABS. They come in brass, CPVC or PVC. CPVC valves are recommended for temperatures over 105° F. Both CPVC and PVC valves are manufactured in the color black. Care must be taken to determine the material, and correct joining and transition methods. ABS pipe shall not be directly glued to CPVC or PVC valve bodies. There are brass valves on the market, but they are not common on gray water systems.
Backwater valves prevent the contamination of the gray water system or surge tank from black water intrusion in the event of sanitary sewer or building drain stoppages.
Backwater valves are designed to be installed in the horizontal position. The use of backwater valves in the vertical position must be installed per the terms of their listing and approved by the AHJ. Equally important is the direction of flow. Many ejector backwater valves are designed for vertical installation, but only when the valve is closed when the pump is not active. Some gray water guidelines portray the valve in the vertical position and stay open unless there is a sewer backup. This installation is not recommended and the valve will not shut properly when required.
Connections to potable and reclaimed (recycled) water systems
Extreme care should be taken to prevent any possibility of gray water, or other nonpotable water, from entering the potable water system. An air gap between the nonpotable and the potable water will ensure contamination will not occur.
Note:A reduced pressure backflow device is not a substitute for an air gap; however, rainwater and tertiary treated reclaimed water provided by a municipal water treatment facility may use a reduced pressure principle backflow device on potable make up water. All other requirements for testing are the same regardless of the alternate water source.
Understanding and mitigating the potential hazards associated with gray water systems makes these issues fairly easy to avoid, and incorporating a gray water system into a building’s design can greatly increase its level of sustainability. Proper installation of the system and its components can help ensure the system operates safely and can prove to be a much more fruitful and realistic plan than, say, planning your retirement around your son’s professional baseball career. But, hey — there are plenty of wealthy artists out there, right? Right?