Provides that any city coterminous with, and comprised only of, an island that relies solely on groundwater aquifers for its potable water source and does not have reasonable access to a potable water source outside its jurisdiction may designate one or more aquifer conservation zones.

Declares that aquifer conservation zones may only be designated for the purpose of conserving and protecting potable water sources.

Authorizes any city to consider whether an area is within an aquifer conservation zone when determining the residential density of that particular area. The residential densities within conservation zones, in combination with other densities of the city, must be sufficient to accommodate projected population growth under RCW 36.70A.110.