Article #1638 - Gray Water for Toilets - Code Notes
Water conservation strategies are sometimes proposed in commercial and residential buildings to meet provisions of sustainable design programs. Gray water recycling is one of these water conservation strategies allowed by the International Plumbing Code (IPC). The IPC, Appendix C, provides guidance on Gray Water Recycling Systems in residential and commercial buildings. It includes provisions to use gray water for flushing toilets (water closets) and urinals as well as for subsurface landscape irrigation. The Uniform Plumbing Code (UPC) only allows gray water to be used in residential subsurface landscape irrigation.
Note that the definitions and code allowances for other water conservation strategies, such as reclaimed water and rainwater, are different from those of gray water. Reclaimed water is domestic wastewater that is suitable for direct use as the result of tertiary treatment¹. The UPC allows reclaimed water for flushing toilets and urinals, in trap primers for floor drains and floor sinks, and in subsurface landscape irrigation systems for nonresidential buildings only. Neither the IPC nor the UPC directly addresses using captured rainwater for flushing water closets and urinals.
Field research shows that it is feasible to move away from traditional plumbing designs, which use potable water in all fixtures, and substitute gray water from bathtubs, showers, lavatories, clothes washers, and laundry trays for flushing water closets and urinals. Gray water plumbing system designs reduce demand on the potable water supply. Key requirements of a gray water plumbing system allowed by the code are that the gray water must be disinfected, must be dyed to differentiate it from potable water, and may not be stored for longer than 72 hours.
Gray Water (IPC Definition)
Waste discharged from lavatories, bathtubs, showers, clothes washers, and laundry trays.
Gray Water (UPC Definition)
Untreated household waste water that has not come into contact with toilet waste. Gray water includes used water from bathtubs, showers, and bathroom wash basins, and water from clotheswashers and laundry tubs. It shall not include wastewater from kitchen sinks or dishwashers.
Reclaimed Water (UPC Definition)
Water that, as a result of tertiary treatment of domestic wastewater by a public agency, is suitable for a direct beneficial use or a controlled use that would not otherwise occur. The level of treatment and quality of the reclaimed water shall be approved by the public health authority having jurisdiction.
Plan Review
Note that the Plan Review and Field Inspection guidance only applies to the provision granted in the IPC for collection of gray water from lavatories, bathtubs, showers, clothes washers, and laundry trays for use in flushing of water closets and urinals.
- Confirm that the collection reservoir is designed to be constructed of durable, nonabsorbent, and corrosion-resistant materials. The reservoir shall be a closed and gas-tight vessel. Access openings shall be provided to allow inspection and cleaning of the reservoir interior.
- Confirm that the distribution piping materials meets one of the standards listed in IPC 2006 Table 605.4.
- Confirm that the gray water entering the reservoir will pass through an approved filter such as a media, sand, or diatomaceous earth.
- Confirm that a full-open valve will be installed downstream of the last fixture connection to the gray water discharge pipe before entering the required filter.
- Confirm that the collection reservoir design will meet the daily flushing requirements of the fixtures, have a maximum retention time less than 72 hours, and be sized to a minimum 50-gallon capacity.
- Check that the collection reservoir is equipped with an overflow pipe having the same or larger diameter as the gray water influent pipe. Check that the drain is located at the lowest point of the collection reservoir and is the same diameter as the overflow pipe. Both the overflow pipe and the drain shall be directly connected to the sanitary drainage system.
- Check that the collection reservoir is equipped with a vent sized in accordance with IPC 2006, Chapter 9, and based on the diameter of the reservoir influent pipe.
Field Inspection
- Confirm that the collection reservoir and distribution piping meets the design criteria.
- Confirm the gray water is disinfected by an approved method that employs one or more disinfectants such as chlorine, iodine, or ozone. Confirm the gray water is dyed blue or green with a food-grade vegetable dye.
- Confirm the distribution piping and reservoirs are identified as containing nonpotable water.
Code Citations*
IPC 2006, Section 301.3 Connections to drainage system.
All plumbing fixtures, drains, appurtenances and appliances used to receive or discharge liquid wastes or sewage shall be directly connected to the sanitary drainage system of the building or premises, in accordance with the requirements of this code. This section shall not be construed to prevent indirect waste systems required by Chapter 8.
Exception: Bathtubs, showers, lavatories, clothes washers and laundry trays shall not be required to discharge to the sanitary drainage system where such fixtures discharge to an approved gray water system for flushing of water closets and urinals or for subsurface landscape irrigation.
IPC 2006, Appendix C, C101.1 Scope:
The provisions of this appendix shall govern the materials, design, construction and installation of gray water systems for flushing of water closets and urinals and for subsurface irrigation.
¹For purposes of this discussion, tertiary treatment shall result in water that is adequately oxidized, clarified, coagulated, filtered, and disinfected so that at some location in the treatment process, the seven day median number of total coliform bacteria in daily samples does not exceed two and two-tenths per one hundred milliliters, and the number of total coliform bacteria does not exceed twenty-three per one hundred milliliters in any sample. The water shall be filtered so that the daily average turbidity does not exceed two turbidity units upstream from the disinfection process.
*Copyright, 2006, International Code Council
, Inc. Falls Church, Virginia. All rights reserved. 2006 International Residential Code.
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