PDFWAC 246-291-210
Distribution systems.
(1) Storage reservoirs shall be designed to:
(a) Prevent entry by birds, animals, insects, excessive dust, and other potential sources of external contamination;
(b) Include:
(i) A weathertight roof;
(ii) A lockable access hatch;
(iii) A screened roof vent;
(iv) An overflow pipe with atmospheric discharge or other suitable means to prevent a cross-connection;
(v) A sample tap;
(vi) A drain to daylight, or an alternative design approved by the department or health officer that is adequate to protect against cross-connection;
(vii) Tank isolation in order to perform maintenance procedures; and
(viii) Other appurtenances appropriate for the protection of stored water from contamination;
(c) Be above normal ground surface level. If the bottom elevation of a storage reservoir must be below normal ground surface:
(i) The storage reservoir must be placed above the groundwater table; and
(ii) The top of a partially buried storage reservoir must be at least two feet above normal ground surface.
(2) A Group B system designed to supply fire hydrants must have a minimum distribution main size of six inches (150 mm) supplying each hydrant.