Workers arriving at the State Archives Friday morning in Olympia found several inches of water on the floor.
The secretary of state's office says a water supply line leaked overnight.
Most of the damage was on the main entry floor of the building, which is across a street from the Capitol.
Some water dripped to the floor below and damped hundreds of volumes holding marriage records and other documents from southwest Washington. Some property photos and leather-bound county journals were damp.
State workers are cleaning up and drying things out. Fans and dehumidifiers will run through the weekend.
Deputy State Archivist Terry Badger says no records will be ruined.