The electrical conductivity of water is usually measured by conductivity, the higher the conductivity, the higher the concentration of dissolved ions in the water. The conductivity of water is not only affected by the dissolved substances in the water, but is also closely related to the temperature, pH and dissolved minerals or pollutants in the water.
What is the Conductive of Water?
Water is electrically conductive because it contains dissolved ions that can carry an electrical charge. Ions are usually charged particles such as cations (positively charged ions) and anions (negatively charged ions). The ability of water to conduct electricity depends on the concentration of these ions in the water.
What is Conductivity?
Electrical Conductivity (EC) is a measure of the ability of water or other solutions to conduct an electric current, and represents the concentration of dissolved ions in a solution. In other words, conductivity reflects how many ions in the water are able to carry an electrical charge and thus conduct an electric current. Conductivity is usually measured in microsiemens per centimetre (µS/cm) or millisiemens per centimetre (mS/cm).
Conductivity is denoted by the Greek letter ρ.
σ = 1/p
- σ = conductivity
- ρ = resistivity
Reasons for the High Conductive of Water
- Salinity
- Water flow
- Temperature
Conductivity and Salinity
Salts are the main source of conductivity in water. When salts such as sodium chloride (NaCl), calcium chloride (CaCl₂), and sodium sulfate (Na₂SO₄) are dissolved in water, they dissociate into ions (e.g., Na⁺, Cl-, Ca⁺, SO₄², etc.), which are able to flow freely in water, resulting in an increase in conductivity. – etc.), these ions are able to move freely in the water, resulting in an increase in the conductivity of the water.
The very high conductivity of seawater is mainly due to its high content of dissolved salts, especially sodium chloride and magnesium chloride.
Conductivity and Water Flow
Conductivity and water flow rate are two independent parameters, but they may affect each other or reflect changes in water quality in some cases. In the treatment process, water flow rate may affect the ion concentration in the water, and changes in conductivity can be used as one of the indicators to measure the effectiveness of treatment. For example, in the reverse osmosis (RO) water treatment system, water flow and conductivity changes are closely related to the flow rate being larger, which may lead to the passage of more dissolved substances, and conductivity can reflect the removal of dissolved substances.
Conductivity and Temperature
Water temperature has a significant effect on conductivity. As the temperature increases, the ionic activity in the water intensifies, resulting in an increase in the water’s ability to conduct electricity. As a result, conductivity usually increases with increasing water temperature. The conductivity of a body of water may be higher at higher temperatures. For every 33.8 °F (1 °C) increase in temperature, the conductivity increases by 1.9%, so it is important to measure both temperature and conductivity to compare measurements.
How to Measure Conductivity?
Measuring the conductivity of water is usually done by measuring the electrical conductivity. Conductivity reflects the concentration of dissolved ions (e.g., salts, minerals, etc.) in the water that are capable of conducting electrical currents.
Use of Conductivity Meter
A conductivity meter is a standard tool for measuring the electrical conductivity of water. It directly measures the conductivity of a water sample, usually in microsiemens per centimetre (µS/cm) or millisiemens per centimetre (mS/cm). The conductivity meter is calibrated using a standard solution, usually 1413 μS/cm or 12,880 μS/cm. This ensures the accuracy of the measurement results. The temperature of the water affects the conductivity measurement, so modern conductivity meters often have Automatic Temperature Compensation (ATC), which automatically adjusts the conductivity reading for changes in temperature.
Use of Conductivity Electrode Probes
Conductivity probes are used in conjunction with a conductivity meter to measure the electrical conductivity of water by inserting it into a water sample and the flow of current between two electrodes on the probe.
These probes can display a conductivity reading through the conductivity meter and are often used in conjunction with a conductivity meter to provide more accurate results.
Using Conductivity Test Strips
- Conductivity Test Strips are a convenient, low-cost measurement tool that can be used in situations where precise measurements are not required.
- The paper is immersed in a sample of water and a colour change occurs on the paper. By comparing it with the colour chart on the package, the conductivity range of the water can be estimated.
Multi ParameterWater Quality Monitoring Cabinet
Multi-parameter instruments can be used to measure conductivity. Multi-parameter instruments are devices that can measure multiple water quality parameters simultaneously. They usually integrate multiple sensors and can be used to monitor a number of parameters such as pH, dissolved oxygen (DO), oxidation reduction potential (ORP), turbidity, salinity, temperature, and more.
Reduces the Conductive of Water
- Lowering the conductivity of water is achieved primarily by reducing the concentration of dissolved ions in the water. These ions are the source of salts, minerals or contaminants in water, so the key method of reducing conductivity is to remove them.
- Use of reverse osmosis (RO) systems
Reverse osmosis is a highly efficient water treatment method that removes most of the dissolved ions in water, including salts, minerals, and some contaminants, through a semi-permeable membrane. Water treated by reverse osmosis usually has a very low conductivity and is close to pure water. - Ion Exchange
Ion exchange is another method of removing dissolved ions from water. Ions such as calcium (Ca²⁺), magnesium (Mg²⁺), and sodium (Na⁺) ions are exchanged with hydrogen (H⁺) or sodium (Na⁺) ions in exchange resins to remove hardness ions and reduce conductivity. Hardness ions and reduce conductivity. - Coagulation and precipitation
Coagulation is the process of adding a coagulant (e.g., aluminium or iron salts) to water to cause suspended or partially dissolved substances or pollutants to aggregate and form particles, which are ultimately removed by precipitation. This method reduces the dissolved solids and certain ions in the water, thus lowering the conductivity. - Removal of pollutants from water
Pollutant removal: Pollutants in water, especially heavy metals, pesticides, chemical pollutants, etc., usually increase conductivity. Removing these pollutants from water through physical or chemical methods (e.g., precipitation, adsorption, chemical reactions, etc.) can effectively reduce conductivity. - Mixed water
If the conductivity in a water source is too high, it can be mixed with water of low conductivity to reduce the overall conductivity by dilution. For example, if the conductivity of industrial or other water sources is too high, the overall conductivity can be reduced by introducing water with low conductivity.
Summary
Water conductivity is a key water quality indicator. By measuring conductivity, we can better understand water quality conditions and ensure water safety and suitability. Controlling water conductivity is an important step in water quality monitoring and water treatment processes to ensure the quality of the water source.
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