By Kayla Lorday | Updated Mar 24, 2022
Water conductivity measures the capacity of water to conduct electrical current, quantified in siemens per centimeter (S/cm). It depends on the presence of dissolved ions—both negatively charged (chloride, nitrate, phosphate, sulfate) and positively charged (aluminum, calcium, magnesium, iron, sodium). Temperature also plays a role; at higher temperatures ions move more freely, so 25 °C is the standard reference for conductivity measurements.
Chlorine (Cl₂) is a potent oxidizing agent widely used as a disinfectant. In water at pH ~7 it forms hypochlorite ions (OCl⁻), the active component in household bleach. While chlorine itself is highly toxic in gaseous form, its dissolved ions contribute significantly to total dissolved solids—about 70 % of the conductivity measured in S/cm.
Natural chlorine is most commonly found as sodium chloride (NaCl), which accounts for roughly 1.9 % of seawater’s mass. The concentration of chloride ions directly influences conductivity: higher chloride levels yield higher conductivity. In the United States, surface water conductivity ranges from 50 to 1,500 µmhos/cm, while inland freshwater lakes typically measure between 150 and 500 µmhos/cm.
During municipal water treatment, a measured amount of chlorine is added to kill microorganisms before distribution. This addition increases the total dissolved solids and thus raises the water’s conductivity. Elevated conductivity can affect taste and overall water quality. Conversely, as people treat water by removing inorganic ions, conductivity steadily declines.
• Conductivity is a reliable proxy for total dissolved solids and ion concentration.
• Chlorine, while essential for disinfection, increases conductivity by adding electrolytes.
• Monitoring conductivity helps assess treatment efficacy and ensure potable water meets quality standards.
