Water can be present in a surface separator during production, either from liquid water in the zone being tested or by condensation from water vapor in the produced gas, or possibly from both. Water from aquifers or seawater may also need to be analyzed in connection with water-injection activities. The analysis of oilfield waters has a wide range of applications, including identifying the origin of produced water, characterizing aquifer properties, interpreting wireline-log measurements, predicting formation damage from water incompatibility, investigating scaling tendencies in surface and downhole equipment, monitoring fluid movement in reservoirs, identifying the presence of bacteria, evaluating disposal options and environmental compliance, and predicting and monitoring corrosion. Water analyses also can be useful in diagnosing and correcting numerous oilfield operating problems. The American Petroleum Institute (API) publishes Recommended Practice 45, which contains information on the applications of oilfield-water analyses and gives recommendations for the proper collection, preservation, and labeling of oilfield-water samples.