(1) Each applicant for a building permit of a building needing potable water shall provide evidence of an adequate water supply for the intended use of the building. Local regulations should be designed to produce enough data to make such a determination, addressing both water quality and water quantity issues. RCW 19.27.097 provides that such evidence may be in the form of a water right permit from the department of ecology, a letter from an approved water purveyor stating the ability to provide water, or another form sufficient to verify the existence of an adequate water supply.

(2) Requirements under RCW 90.94.020 and 90.94.030 apply to counties and cities reviewing water adequacy for development.

(3) Counties and cities should give consideration to guidelines promulgated by the departments of ecology and health on what constitutes an adequate water supply.

The department of health regulates the maximum number of equivalent residential units (including each domestic unit within a multifamily development) that can be legally and physically served by each public water system. Each water system tracks the current number of available equivalent residential units.

(4) If the department of ecology has adopted rules on this subject, or any part of it, local regulations must be consistent with those rules. Such rules may include instream flow rules, which may limit the availability of additional ground or surface water within a specific geographic area.

(5) Counties and cities may impose conditions on building permits requiring connection to an existing public water system where the existing system is willing and able to provide safe and reliable potable water to the applicant with reasonable economy and efficiency.