The electrical conductivity of a solution is a measure of the ability to conduct electrical current. Because the electrical current is conducted via the ions in the solution, the conductivity increases as the concentration of ions do. This is why electrical conductivity is generally used as a surrogate measure for total dissolved solids concentration. Therefore, one of the primary uses of electrical conductivity is determining the suitability of a water, such as treated wastewater, for irrigation. In addition, conductivity can be used to indicate industrial spill event in source water monitoring applications and in-process spill and leakage events in industrial wastewater monitoring applications. The SI unit for conductivity is millisiemens per metre (mS/m) but in water and wastewater applications it is common to use microsiemens per centimetre (µS/cm) as well.