In 1964 the Bureau of the Budget (now the Office of Management and Budget) issued Circular A-67 to coordinate water data acquisition activities by federal agencies. Under Circular A-67 the Department of the Interior's Office of Water Data Coordination (OWDC) has the responsibility to (1) maintain a catalog of information on water data, (2) undertake a continuing review of water data requirements, (3) prepare a federal plan for efficient utilization of water data activities, and (4) design a national water data network. A concept of three levels of information was developed as the rationale for national network planning. The three levels are level I, a base level of information for national and regional planning and assessment; level II, data needs for subregional planning and assessment; and level III, data for operation and management at the local level. Several elements of level I of the national network have been totally or partially implemented, including (1) the streamflow and stream quality accounting elements, (2) the water use accounting element, (3) the water quality surveillance element, and (4) the flood surveillance element. The National Water Data Network is coordinated through an interagency process involving more than 30 federal agencies and numerous nonfederal organizations interested in water data acquisition. As part of this coordination process the Catalog of Information on Water Data is maintained and is used as the basis for planning and operation of the network. Through the National Water Data Exchange, established as an outgrowth of the coordination activity, the water data information base is being expanded continually.