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Gray Water Systems.
The Uniform Plumbing Code identifies three types of gray water systems: 1) subsurface irrigation where drip emitters are buried 2 inches below finished grade; 2) subsoil irrigation where large diameter pipe is buried in deep trenches to permit deep root irrigation and rapid dispersal of gray water; and 3) 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 (BOD), 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; 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.
© 2016 International Association of Plumbing and Mechanical Officials