Water control and improvement districts were authorized by the Texas legislature in 1925 and 1927 to provide broader powers than those allowed the water improvement districts. The water control and improvement districts organized under the 1917 conservation amendment may engage in flood control, irrigation, drainage, reclamation, preservation of water resources, development of forests, development of hydroelectric power, navigation, and sewage disposal. Those operating under the 1904 amendment are more limited but may provide irrigation, drainage, navigation, and prevention of overflows. The districts can consist of a single county or more than one county. Organization and debt limitation are similar to those for water improvement districts. An elected board of five directors oversees the district's activities, including construction projects, financing, and legal right-of-ways. Tax bases are slightly different in that they not only may use either the ad valorem or specific benefits basis but also may combine the two. In 1929 the legislature authorized the state board of water engineers to establish master districts composed of two or more water control and improvement districts to control the water of a particular stream and to coordinate the district's activities. Such districts have separate taxing powers, apart from those exercised by the individual districts. Districts that encompass at least 30,000 people and an estimated real estate value of $50 million may become municipal districts. By the latter part of the twentieth century water control and improvement districts were among the most popular and commonly used entities. They were criticized, however, for being largely financing mechanisms for large-scale developers and focusing much less attention on the management of water resources. The largest concentration of districts was in the Houston area, though there was also a considerable number in other urban areas across the state, including San Antonio, Austin, and Brownsville. In 1992 211 water control and improvement districts were registered with the Texas Water Commission.