Plumber's Licensing Exam: Gray-Water Recycling

Gray-water recycling may be the next big thing for our (usable) water-hungry planet. The technology has been developing in fits and starts, but these systems haven’t achieved widespread popularity as of yet. Gray water from bathing, laundry, and dish washing is estimated to comprise 50% to 80% of residential wastewater. Inspectors must ensure that onsite treated non-potable systems are only being used in installations that are specifically allowed by the authority having jurisdiction.
Installers and inspectors must have a clear understanding of the fixtures allowed in a gray water system. Due to the growing popularity of water conservation, there is an increased demand in the plumbing industry to install systems that promote sustainability. The potential water savings are obviously substantial. Think about it: with a full-fledged gray-water recycling system, you could flush all the water closets and urinals and still supply the water you need for landscaping without putting any demand on the potable water system—it’s like “free” water. The main drawback is the added expense of installing such a system and the extra room it takes up. However, it is quite possible that gray-water recycling systems will become more prevalent with the continued over - population of the world.

Objectives
- Identify applications for gray-water recycling
- State the requirements of a safe and effective gray-water recycling system
- Apply system sizing guidelines
- Distinguish the differences and similarities of water closet and urinal flushing systems as compared to landscape irrigation systems

Key Term:
black water

What Is Gray-Water Recycling?
The two basic types of drainage water that go into the sanitary drainage system of a building are often referred to as gray water and black water.

Gray water is the drainage from tubs, showers, lavatories, and laundry facilities. Black water is the discharge from water closets, bidets, and urinals. Black water contains human bodily waste.

Gray water does not have the disease-carrying capability of black water, even though it is certainly not potable. The discharge from kitchen sinks and other food preparation fixtures cannot be included in the gray-water category because of the organic (food) waste that it carries. Food waste decomposes and would foul a gray-water recycling system. (Refer to IPC Commentary Appendix C: Introduction)

Gray-water recycling systems are simply an effective means of saving precious water resources by reusing the water that runs down the drains from showers, baths, lavatories, automatic clothes washers, and laundry trays. Even though this is not potable water, it is not contaminated to an excessive or dangerous degree. After filtering to prevent clogging of any parts of the gray-water distribution system, gray water flushes fixtures and waters landscaping just as well as water drawn from the potable water system.

Figure below shows how a typical gray-water recycling system is set up. This type of system shall be designed by a person registered or licensed to perform plumbing design work. Components, piping, and fittings used in an alternate water source system such as this one shall be listed.

Real-Life Situation: Julio and Pat are roughing in a new house that will have a gray-water recycling system. This is the first time Ace Plumbing Company is installing one of these systems, but it is a field in which Carlos, Ace’s owner, sees growth potential. Green construction techniques will continue to develop. Which fixtures should Pat and Julio drain to the gray-water reservoir? Sophia, the Ace Plumbing Company estimator, has sized the gray-water reservoir to hold 100 gallons for this four-bedroom colonial, which will have two full bathrooms. How can the installers double check to be sure the system is sized correctly? After all, this is the first time for Sophia, too.


Figure: Typical Gray-Water Recycling System

Fact: The U.S. Environmental Protection Agency (EPA) estimates that 15% of the fresh, potable water used in the United States is used for irrigation. Gray water can easily be used for irrigation purposes and save some of that potable water for human and animal consumption.

Connections
This section of the code (Ref: UPC 1602.3) makes it very clear that under no circumstances shall a gray water system be directly connected to a potable water supply. In the IPC, Section 301.3 requires all fixtures to be connected to the sanitary system of the building. This rule precludes the installation of a gray-water recycling system because some of a building’s fixtures must be connected to the gray-water drainage system and completely avoid the sanitary drainage system. If the jurisdiction you are testing in supports gray-water recycling, the local code must have amended this rule to allow for gray-water recycling. As with any installations, it is important to first check your local code. (Refer to IPC 301.3, C101.1–C101.14)
Alternate water sources for non-portable applications require inspections at regular intervals. A maintenance log is required to have a permit and shall be maintained by the property owner and be available for inspecting. In general, all the same rules apply to gray-water piping systems as standard piping systems. Permitting rules are similar. The materials used must meet the same quality and design criteria as potable water distribution systems and sanitary drainage systems. The testing of systems and inspections by the Authority Having Jurisdiction are all the same.
All gray-water distribution piping must be labeled as such using black letters on a yellow background. Whenever non-potable waters systems are installed, including outside of the building, the piping must be identified. Also, the water drained from appropriate fixtures must be gathered and stored in a reservoir so a supply is available for pumping to the fixtures that will use the gray water.
Gray water carries debris with it that must be filtered out before the water can be pumped to any fixtures. This can be accomplished through a variety of filtration methods. Since we can expect that the dirt load will be fairly heavy, the system must have a back-washing feature, and the discharge from the backwash filter must drain directly to the sanitary drainage system. In order for a backwashing procedure to be effective and safe, the gray-water drain must have a full-opening valve in it just before the gray-water filter. The valve must be closed before backwashing or maintenance can be carried out. In addition, all fixtures must be tagged as “out of service” to prevent an overflow while the valve is closed.

Water Closets
(Refer to IPC C102.1–C102.6)

Storage
Sizing a gray-water reservoir for a water closet and urinal flushing system requires some thought and advanced planning. You want to ensure that there will be enough water to meet the flushing needs of the building, without storing it for so long that organic debris in the water begins to decay and cause odors. The target for a maximum retention time is 72 hours. (Refer to IPC C102.1)
The IPC requires the gray-water reservoir to hold twice the daily requirement of water sufficient to flush the fixtures, with a minimum size of 50 gallons. Therefore, we must aim for a reservoir size that falls between a 2-day supply and a 3-day (maximum) supply. To calculate the requirements for a residence, you count the bedrooms and estimate that there will be two people in one bedroom and one person in each of the other bedrooms. Multiply the number of people by 7 to get an approximation of the total number of flushes per day. Multiply the “flushes per day” number by the gallons per flush of the fixture(s). Multiply that number by 2. That will be the reservoir capacity required, as long as it is at least 50 gallons.

Example: Let’s look at an example using a single-family home that has four bedrooms and 1.6 GPF water closets.

The installation, construction, alteration, or repair of rainwater catchment systems, intended to supply uses such as water closets, urinals, trap primers for floor drains and floor sinks, irrigation, industrial processes, water features, cooking tower makeup and other uses, shall be approved by the authority having jurisdiction.

Disinfection
The water that is stored for flushing water closets and urinals must be disinfected after the filter. Disinfection reduces the possibility of a buildup of bacteria in the reservoir and prevents odors. The disinfection process is not intended to make the gray water potable. (Refer to IPC C102.2)

Dye
Gray water must be dyed blue or green before it is pumped to the water closet(s) and/or urinal(s) it supplies. This identification will make it clear to any user of the fixture that the water is not intended for consumption. The dye must be food-grade to ensure that no chemical enters the system that could damage any part of the system. (Refer to IPC C102.4) Gray water systems shall be marked in accordance with this section with the words, “Caution: Nonpotable gray water, do not drink” in yellow letters.
 

Makeup Water
The reservoir must have makeup water introduced into the reservoir as necessary from the potable water supply. Preventing gray water from migrating into the potable water supply system is critical. Therefore, the best way to prevent this is with a reduced pressure principle backflow preventer on the potable water supply. (Refer to IPC C102.3)

Tips
Before you begin the installation of a gray-water recycling system, discuss the job with the local Authority Having Jurisdiction. Even though the owner may have a permit for the installation, some localities limit the allowable uses for the gray water. Some jurisdictions limit gray-water use to underground irrigation. Others may permit surface irrigation, but only by the flood method, with no spraying allowed. There are very small quantities of human waste in bath water, which causes concern if the water is untreated.

Landscape Irrigation
The size of a reservoir for a subsurface irrigation system must be calculated estimating retention of the gray water for no more than one day. Sizing is done in the same general way as for a water closet and urinal flushing system, except the capacity stays at the single-day volume. Since disinfection of irrigation water is not required, bacteria and odors would grow quickly in water retained longer than a day. If there is excess gray water, it can be wasted to the sanitary drainage system or the rate of irrigation can be increased. If there is not enough gray water produced, watering can be reduced. (Refer to IPC C103.1–C103.10)

This type of system would be used where the irrigation is controlled by a timer. If the crop or landscaping is estimated to need 50 gallons per day, then a 50-gallon tank would be the size required. Remember, gray water for irrigation does not require treatment so the tank must be emptied daily, either to the irrigation system or, when rainfall or changing irrigation needs decrease, to the sanitary drainage system.

Caution: Gray water, especially from laundry sources, tends to be alkaline (high pH) in nature because of the soaps and detergents. Many plants and crops thrive in an alkaline environment, but others grow better in acidic soil. Before installing a gray-water system, find out the preferred pH level for the crop(s) that will be irrigated so that the pH can be adjusted through treatment, if necessary.
The gray-water piping and reservoir must be labeled as nonpotable water to prevent anyone from piping a cross-connection by mistaking the gray water for a potable water supply. There is no requirement for dye to be added to a subsurface irrigation system since the water is not visible or available for the public to use mistakenly as potable water.
On the outlet of the reservoir, a full-opening valve and a check valve must be installed to prevent backflow from entering irrigation pipes. No makeup water is required on irrigation systems. If makeup water is connected, it must be done in a way that prevents backflow. As with the gray-water recycling system from the water closet, the reduced pressure principle backflow preventer is the best choice.