During hydrocarbon production, water is typically co-produced from the geologic formations producing oil and gas. Understanding the composition of these produced waters is important to help investigate the regional hydrogeology, the source of the water, the efficacy of water treatment and disposal plans, potential economic benefits of mineral commodities in the fluids, and the safety of potential sources of drinking or agricultural water. In addition to waters co-produced with hydrocarbons, geothermal development or exploration brings deep formation waters to the surface for possible sampling. This U.S. Geological Survey (USGS) Produced Waters Geochemical Database, which contains geochemical and other information for produced water and other deep formation water samples of the United States, is a provisional, updated version of the 2.3 USGS Produced Waters Database (Blondes and others, 2019).