Conductivity is the measure of a material’s ability to conduct an electric current. In liquids, it indicates the presence of dissolved ions, such as salts, acids, or bases, which allow electricity to flow. Conductivity is a critical parameter in industries like water treatment, chemical processing, environmental monitoring, and manufacturing, as it helps assess water purity, chemical concentrations, and process efficiency. Understanding conductivity is essential for ensuring the quality and safety of fluids used in various applications.

What is conductivity?

Electrical conductivity measures the ability of water to conduct electricity, which provides a measure of the substances dissolved in the water. It is the opposite of resistance. Pure, distilled water is a poor conductor of electricity. When salts and other inorganic chemicals dissolve in water, they break down into tiny electrically charged particles called ions. Ions increase the ability of water to conduct electricity. Common ions in water that conduct electricity include sodium, chloride, calcium and magnesium. Because dissolved salts and other inorganic chemicals conduct electrical currents, conductivity increases with increasing salinity. Organic compounds, such as sugars, oils and alcohols, do not form conductive ions.

Conductivity Applications

  • Water treatment and purification: Monitor water purity, control reverse osmosis systems, boiler water quality, cooling tower water quality.
  • Industrial process control: optimize chemical concentrations in chemical, food, pharmaceutical and other industries.
  • Environmental monitoring: detecting pollution of rivers and lakes, monitoring wastewater treatment, preventing salinization of groundwater.
  • Agriculture & Hydroponics: Measure soil salinity, optimize hydroponic nutrient solutions, and prevent salinity build-up in irrigation water.
  • Pharmaceutical & Medical: Ensure Water for Injection (WFI) purity, control infusion, dialysis, conductivity.

Why is conductivity important?

Aquatic animals and plants are adapted to a certain range of salinity. Beyond this range, they will be negatively affected and may die. Some animals can handle high salinity, but not low salinity, while others can handle low salinity, but not high salinity.

In addition to its direct effects on aquatic life, salinity has many other important effects on water chemistry and water density.

Electrical conductivity can be used as a general measure of water quality. Each body of water tends to have a relatively constant range of conductivity that, once determined, can be used as a baseline for comparison with conventional conductivity measurements. Significant changes in conductivity may indicate that a discharge or some other source of pollution has entered an aquatic resource. Often, anthropogenic disturbances tend to increase the amount of dissolved solids entering the water, which leads to an increase in conductivity. Water bodies with elevated conductivity may also have other indicators of impairment or alteration.

How is conductivity measured?

Salinity is most often reported in parts per thousand or the equivalent term grams per liter. For example, the average salinity of seawater is 35 ppt, which is equivalent to adding 35 grams of salt to 1 liter of water

Conductivity is reported in units called Siemens or its smaller version, milliSiemens is one thousandth of a Siemens and microSiemens is one millionth of a Siemens. Most commonly a special type of conductivity is used, called specific conductivity.

Precautions When Measuring Conductivity

Selecting the right conductivity probe

  1. Select the appropriate sensor material (e.g. stainless steel, graphite or platinum electrodes) according to the type of liquid.
  2. High conductivity liquids (e.g. seawater) are suitable for quadrupole electrodes, while low conductivity liquids (e.g. ultrapure water) are suitable for bipolar electrodes.

Temperature compensation

  1. Conductivity is strongly influenced by temperature, so temperature compensation is usually required (e.g. using the ATC automatic temperature compensation function).
  2. It is recommended to use a conductivity meter with a temperature sensor to ensure accurate measurements.

Periodic calibration

  1. Use standard solutions (e.g. 84µS/cm, 1413µS/cm, 12.88mS/cm) for calibration to improve the accuracy of measurement.
  2. Perform single-point or multi-point calibration periodically according to the instrument manual.

Avoid electrode contamination or air bubble interference.

  1. Clean the electrodes to avoid dirt or oil film affecting the measurement.
  2. Ensure that the electrode is fully immersed in the solution during measurement to avoid air bubbles affecting the reading.

Avoid external interference

Avoid electromagnetic interference (e.g., near high-power equipment, motors, etc.), which may affect measurement accuracy.

In industrial applications, it is recommended to use shielded cables to connect the sensor to minimize signal interference.
Effects of flow rate and agitation

Excessive flow rate or agitation may cause measurement fluctuations, it is recommended to stabilize the liquid flow before measurement.

When measuring ultrapure water, avoid the dissolution of CO₂ in the air, which may cause readings to deviate.
Maintenance and Storage

When not in use for a long period of time, the electrode should be stored in a suitable solution to prevent drying out and damage.

Avoid storing the conductivity meter in extreme temperatures or corrosive environments to prolong equipment life.

Conductivity technology

Both conductivity and salinity are measured by an electrical probe on the data logger. This probe measures how much current is passing through the water. The salinity is then calculated from that value.

Conductivity is determined by measuring how easy it is for the current to flow between two metal plates. These metal plates are called electrodes and are spaced a specific distance apart. The dissolved salt in the solution is attracted to the plate with the opposite charge. In many probes, a four-electrode cell is used. Two of the electrodes measure the current of the solution, while the other two electrodes maintain a constant current between them and are used as a reference.

The best method to determine salinity is chemical analysis of the concentration of different ions in water, such as calcium, sodium, chloride and carbonate. However, since this method is time consuming, tedious and expensive, salinity is estimated based on electrical conductivity. Because salt in water conducts electrical currents, the conductivity will be proportional to the salt concentration. Data loggers use a complex mathematical equation to estimate salinity from conductivity. This equation accounts for the temperature dependence of conductivity.

More articles on electrical conductivity:

Conductivity: How to convert mS/cm to uS/cm
How does ph conductivity meter work?
What is pH sensor & How does it work?
What is a pressure transmitter?