The Revised Code of Washington is the topical compilation of Washington state laws. Session law citations are located at the end of each section in brackets. This will tell you when the statute was originally enacted and the subsequent amendments, if any.
Example:
In some cases, the legislature will include a section describing the general legislative intent. Such a section will most likely be found at the beginning of the chapter. The section is sometimes called "legislative findings, intent" or "legislative findings, purpose".
The session laws of Washington are published in the Session Laws of Washington and contain the bill number and the text of bills as passed by the state legislature. The bill number is listed in the table of contents or you can find it on the first page of the relevant chapter (in brackets). This publication is helpful in determining what text was added, amended or deleted by the legislature during the particular session.
PDF: HeinOnline (coverage varies by state).
Microfiche: Law Library, Micromedia room, 2nd floor (coverage varies by state).
Print: Some older session laws for some states are available at the Gallagher Law library at the UW School of Law (coverage varies by state and is very limited-check catalog).
PDF: State legislature websites may link to PDF versions of state statutes. The Law Librarians' Society of Washington D.C. maintains a list of links to state statutes (coverage varies by state).
Microfiche: Law Library, Micromedia room, second floor (coverage varies by state).
Print: Annotated versions of state statutes, which may be official, and some older editions of the official statutes of certain states are available in the Reference stacks on the 2nd floor of the Law Library (coverage of older editions varies by state).