Irrigation systems include but are not limited to agricultural, residential, and commercial applications. The VDH classifies lawn sprinkler systems and irrigation systems as a high hazard; sprinklers, bubbler outlets, emitters, and other equipment are exposed to substances such as fertilizers, fecal material from pets or other animals, pesticides, or other chemical and biological contaminants and pollutants. Sprinklers may remain submerged underwater after use or storms. Should the water system pressure suddenly decrease, such as in the case of a water main break, line flushing, or during a major fire involving multiple fire hydrants, these harmful substances can be back-siphoned into the water distribution system. They may be subject to various onsite conditions such as additional water supplies, chemical injection, booster pumps, and elevation changes. All of these conditions must be considered when determining backflow protection. Some hazards relating to irrigation systems are:
Fertilizers: Ammonia salts, ammonia gas, phosphates, potassium salts.
Herbicides: 2,4-D, dinitrophenol, 2,4,5-T, T-pentachlorophenol, sodium chlorate, borax, sodium arsenate, methyl bromide
Pesticides: TDE, BHC, lindane, TEPP, parathion, malathion, nicotine, MH and others
Fecal matter: Animal (domestic and non-domestic)