The Department of Water managed all water resources, including the availability and quality of water sustainability, throughout Western Australia.

The Department was formed following a revision of Government focus on water resources, taking over many of the functions of the Water and Rivers Commission under delegation.

The Office of Water Strategy was transferred to the Department of Water from the Department of Premier and Cabinet on 1 July 2006.

The proclamation on 31 January 2008 of the Water Resources Legislation Amendment Act 2007 formally abolished the Water and Rivers Commission and transferred all functions to the Minister for Water Resources and the Department of Water from 1 February 2008.

As part of a series of Machinery of Government changes effective 1 July 2017, the Department of Water was amalgamated with the Department of Environment Regulation and the Office of the Environmental Protection Authority to form the Department of Water and Environment Regulation.