International Plumbing Code 2012 (IPC 2012)

The provisions of Chapter 13 shall govern the materials, design, construction and installation of gray water systems for flushing of water closets and urinals. See Figure 1301.1(1).

FIGURE 1301.1(1)

In addition to the provisions of Section 1301, systems for flushing of water closets and urinals shall comply with Section 1302. Except as provided for in this chapter, all systems shall comply with the provisions of the other chapters of this code.
Above-ground drain, waste and vent piping for gray water systems shall conform to one of the standards listed in Table 702.1. Gray water underground building drainage and vent pipe shall conform to one of the standards listed in Table 702.2.
Drain, waste and vent piping for gray water systems shall be tested in accordance with Section 312.
Gray water systems shall be inspected in accordance with Section 107.
Only connections in accordance with Section 1302.3 shall be made between a gray water recycling system and a potable water system.
Gray water recycling systems shall receive only the waste discharge of bathtubs, showers, lavatories, clothes washers or laundry trays.
Gray water shall be collected in an approved reservoir 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.
Gray water entering the reservoir shall pass through an approved filter such as a media, sand or diatomaceous earth filter.
A full-open valve shall be installed downstream of the last fixture connection to the gray water discharge pipe before entering the required filter.
The collection reservoir shall be equipped with an overflow pipe having the same or larger diameter as the influent pipe for the gray water. The overflow pipe shall be trapped and shall be indirectly connected to the sanitary drainage system.
A drain shall be located at the lowest point of the collection reservoir and shall be indirectly connected to the sanitary drainage system. The drain shall be the same diameter as the overflow pipe required in Section 1301.10.
The reservoir shall be provided with a vent sized in accordance with Chapter 9 and based on the diameter of the reservoir influent pipe.
The holding capacity of the reservoir shall be a minimum of twice the volume of water required to meet the daily flushing requirements of the fixtures supplied with gray water, but not less than 50 gallons (189 L). The reservoir shall be sized to limit the retention time of gray water to a maximum of 72 hours.
Gray water shall be disinfected by an approved method that employs one or more disinfectants such as chlorine, iodine or ozone that are recommended for use with the pipes, fittings and equipment by the manufacturer of the pipes, fittings and equipment.
Potable water shall be supplied as a source of makeup water for the gray water system. The potable water supply shall be protected against backflow in accordance with Section 608. There shall be a full-open valve located on the makeup water supply line to the collection reservoir.
The gray water shall be dyed blue or green with a food grade vegetable dye before such water is supplied to the fixtures.
Distribution piping shall conform to one of the standards listed in Table 605.4.
Distribution piping and reservoirs shall be identified as containing nonpotable water. Piping identification shall be in accordance with Section 608.8.