Establishes the one Washington water act.

Requires a city, with a population greater than one hundred thousand, to prepare an environmental impact statement in order to evaluate the past, present, and future environmental impacts of water withdrawals associated with domestic water consumption by the inhabitants of the city, before issuing a building permit for a building necessitating potable water.

Prohibits a municipal water supplier, that supplies water to a city with a population greater than one hundred thousand, from: (1) Delivering more than three hundred fifty gallons per day to a single-family residence located within the city;

(2) Delivering more than one hundred fifty gallons per day per residence to an apartment building, townhome, condominium, or other multifamily residential building located within the city; and

(3) Supplying water in a way that results in the water being discharged from a publicly owned treatment works into a water resource inventory area that is different from the water resource inventory area in which the water originated.