The U.S. Geological Survey (USGS) has a long history of monitoring and research on thequantity and quality of water in our rivers, lakes, and aquifers. Some of this work is doneon a national scale, and some is done on a smaller scale, in cooperation with otherfederal, state, tribal, or local governments. As states, tribes, and utilities have beenassessing their source water, many have found that USGS data and research are helpful inthe process. This paper summarizes the types of sourcewater information available from the US Geological Survey and includes relevant world wide web site addresses.