In Washington State, prospective water users must obtain authorization in the form of a water right permit or certificate from the Department of Ecology (Ecology) before withdrawing groundwater. The groundwater permit exemption allows the users of small quantities of groundwater to construct wells and develop their water supplies without first obtaining a water right permit from Ecology.
The only exceptions to the permit requirement is for withdrawals of groundwater for:
Providing water for livestock (no gallon per day limit).
Watering a non-commercial lawn or garden one-half acre in size or less (no gallon per day limit, however limited to reasonable use).
Providing water for a single home or groups of homes (limited to 5,000 gallons per day).
Providing water for industrial purposes, including irrigation (limited to 5,000 gallons per day but no acre limit).
Department of Ecology
The permit exempt wells webpage expands on the topic. Of particular note, are the publications listed down the right-hand side of the page.
Wells - Licensing, Construction and Reporting
The licensing, construction and reporting page will assist a private homeowner with the process of drilling a well. It includes a notice of intent form which is required even for permit exempt wells. It also includes a link to the Washington State well log report search and review.
Private Wells: Information for Owners
A collaborative Department of Health and Ecology publication, this document (PDF) includes water testing information.