Sometimes called a check valve or a backflow preventer, a chemigation valve is an apparatus designed to protect water supplies from agricultural chemicals used during chemigation, the application of chemicals such as fertilizers and pesticides through irrigation water.^[1] Most chemigation valves consist of a spring-loaded check valve, a low pressure drain, an air and vacuum relief valve, and an injection port for introducing the chemicals downstream of the check valve. Many chemigation valves also have a 4-inch inspection port so that a person can reach inside and feel if the check valve is still functional^{[citation needed]}. Some governments require the use of two chemigation valves installed in series if hazardous chemicals are to be injected^{[citation needed]}.

The following policies require or encourage the installation of these valves:

Texas State law Chapter 344.73 in Subchapter D - 1.(b)^{[citation needed]}

"An irrigation system which adds any chemical is considered to be a 'high health hazard'. Such an irrigation system must not be connected to any potable water supply except through a reduced pressure principle backflow prevention assembly."

Florida's Department of Agriculture and Consumer Services Water Quality/Quantity Best Management Practices for Florida Specialty Fruit and Nut Crops ^[2] p. 20 specifies that:

"Backflow prevention should include a check valve between the irrigation pump and the injection device to prevent backward flow; a low-pressure drain to prevent seepage past the check valve; a vacuum relief valve to ensure that a siphon cannot develop; and a check valve on the injection line."