California Code, Health and Safety Code - HSC § 114213

(a) Any potable water or wastewater tank mounted within a mobile food facility or mobile support unit shall have an air vent overflow provided in a manner that will prevent potential flooding of the interior of the facility.

(b) If provided, a water tank vent shall terminate in a downward direction and shall be covered with 16 mesh per square inch screen or equivalent when the vent is in a protected area or a protective filter when the vent is in an area that is not protected from windblown dirt and debris.