Conductivity is a measure of water's ability to conduct an electrical current, which is directly related to the concentration of dissolved ions. It serves as a rapid proxy for total dissolved solids in water quality monitoring.
Electrical conductivity (EC) in water is determined by the concentration, mobility, and valence of dissolved ions such as sodium, chloride, calcium, magnesium, sulfate, and bicarbonate. It is measured in microsiemens per centimeter (uS/cm) or millisiemens per centimeter (mS/cm) at a standard temperature of 25 degrees Celsius. Pure distilled water has a very low conductivity of about 0.5 to 3 uS/cm, while seawater typically has a conductivity around 50,000 uS/cm. Freshwater streams generally range from 50 to 1,500 uS/cm, with values depending on the local geology and land use. Conductivity is widely used in field surveys because it can be measured quickly with portable probes, providing an immediate indication of water quality changes. Sudden changes in conductivity may signal pollution events such as chemical spills, brine discharges, or stormwater runoff. The relationship between conductivity and total dissolved solids is approximately linear, with TDS (mg/L) roughly equal to conductivity (uS/cm) multiplied by a factor between 0.5 and 0.9.