Before August 6, 1998, this chapter shall not apply to an irrigation canal system if the owner or operator of the system certifies to the department, and notifies each user, in writing, that the water is untreated and is being furnished or supplied solely for agricultural purposes to either of the following:
"Irrigation canal system," as used in this section, means a system of water conveyance facilities, including pipes, tunnels, canals, conduits, pumping plants and related facilities operated to furnish or supply water for agricultural purposes where a substantial portion of the facilities is open to the atmosphere.
Ca. Health and Saf. Code § 116285