(1) If the irrigation system is cross-connected to a public water system, Washington state department of health (DOH) rules (WAC 246-290-490) apply to backflow prevention.

(2) Cross-connections of a fertigation system to any potable water system intended for human use must have either a department of health-approved reduced pressure backflow assembly or reduced pressure detector assembly installed for backflow prevention. Otherwise, a physical separation in the form of an air gap may be used to protect the water source.