Water improvement districts were authorized by the Texas legislature in 1917, replacing the irrigation districts established under the laws of 1905 and 1913. In 1918 the Canales Act allowed such districts to avail themselves of broader taxing powers under the conservation amendment of 1917. Districts could be organized to construct irrigation works, buy improvements already existing, contract for a water supply and distribute it, furnish water for domestic and commercial uses, and cooperate with the United States government under its reclamation laws. The districts were established upon the approval of the state board of water engineers after a majority vote of the qualified tax-paying voters. Cities and towns were not included in a district unless they specifically approved. Each district is governed by a biennially-elected board of five directors who appoint the manager, tax assessor and collector, and a peace officer to enforce the district's regulations concerning sanitation, waste, and recreational activity. Districts organized under the 1917 amendment may issue bonds without limit upon approval of a simple majority of the qualified tax-paying voters and may tax on an ad valorem or a benefits basis. Those operating under the 1904 amendment may issue bonds up to one-fourth of the property values upon approval of two-thirds of the tax-paying voters and may use only the ad valorem basis for taxation. Many water improvement districts were replaced with the formation of the broad-powered water control and improvement districts in the 1920s. In 1992 there were eighteen water improvement districts registered with the Texas Water Commission.