Rights to use public water
Washington's waters belong to the public. Ecology grants a right to use a set volume for a defined purpose in a specific place. Using surface water from a river, stream, spring or lake requires a right no matter how little you take. Customers of a utility don't need their own right if the provider holds one.
Small groundwater uses
RCW 90.44.050 exempts some small well uses from the permit process: stockwatering, a lawn or noncommercial garden of up to half an acre, domestic use up to 5,000 gallons a day, and industrial use up to the same amount. An exempt use that is regularly put to beneficial use carries a right equal to a permitted one. Ecology's Water Rights Search is the place to check what a property holds.
Why this map doesn't show Washington yet
Ecology publishes water rights and their points of diversion in separate tables that have to be joined together, and that work isn't built yet.