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Conductivity is affected by the number of dissolved ions in water (salinity), the types of ions in the water, water flow, rainfall, and temperature.
Conductivity is one of the most useful indicators of water quality. Electrical conductivity measures the ability of water to transmit an electrical current over a certain distance, usually measured in Siemens (S) per distance.
Significant changes in conductivity can be detrimental to water quality and aquatic life. Usually, a sudden increase (or decrease) in conductivity is an indicator of water pollution, generally from agricultural runoff or sewage leakage increasing dissolved solids in the water. According to the World Health Organization (WHO), electrical conductivity values should not exceed 400 microsiemens per centimeter (μS/cm).
In this article, we will cover three common causes of high conductivity in water, how to measure conductivity, and what you can do to decrease conductance.
Three main factors can cause high conductivity in the water:
This is the most common cause of high conductivity. Salinity is an ambiguous term when we talk about the conductivity of water, as salinity refers to the total concentration of all dissolved salts in water.
Electrolytes in water form ionic particles when they dissolve, carrying a positive or negative charge, therefore, making salinity a strong contributor to high conductivity levels.
An increase in the number of dissolved ions in the water causes high conductivity because ions carry electrical charges and are mobile in water. As ions carry an electrical charge, the more ions inside the water, the greater amount of current can be passed through, increasing the conductance level.
It is important to note that ions have different abilities to transmit a charge in water. For example, inorganic ions like sodium (Na+) and potassium (K+) conduct electricity well in water, even though each ion has a different conductive energy.
The size, charge, and ion’s potential to interact with water molecules (H2O) determines if the ions will conduct electricity.
Smaller ions can attract water molecules better than larger ions, however, when small ions bind with H2O they become slow-moving hydrated ions, resulting in moving at the same speed as heavier ions.
For example, lithium (Li+) only conducts electricity half as well as K+ ions, despite its smaller size because Li+ has a stronger interaction with H2O.
Most of the time salinity is not directly measured, but instead, it is obtained from the conductivity reading. This process is known as practical salinity. Just remember that as salinity increases, conductivity increases, and therefore, you should measure the two parameters simultaneously.
Groundwater inflows that are highly mineralized cause high conductivity and salinity levels in the water. Agricultural runoff is the main contributor, flushing high nutrients into water bodies that often carry a higher concentration of dissolved solids, which influence the conductivity of water. Therefore, the higher the water flow volume, the more it affects conductivity and salinity levels.
Rain can also cause high conductivity because it has a higher conductivity level than purified water. Yet, heavy rainfall lowers conductivity as it dilutes the salinity concentration. When salinity levels decrease, so does the conductivity of the water because of the direct relationship they have.
Heavy rainfall often causes flooding, which can increase the conductivity in the water, as salts and minerals from the soil are washed into water sources. However, the effect that flooding has on conductivity depends on the type of water body (freshwater or saltwater) and what ions are present in the surrounding soil.
Although dry seasons do not often see an increase in conductivity, spikes can happen when water first enters a floodplain. Floodplains contain nutrient-rich or mineralized soil that carries ions. So, if the floodplains flood, it will cause high conductivity in the water.
What’s more, high conductivity in water is directly related to rising temperatures because it increases solubility and ionic mobility; ions move faster in warmer water. It is estimated that for every 33.8 °F (1 °C) increase in temperature, conductivity will rise by 1.9%, therefore temperature must be measured alongside conductivity, so that the measurements can be compared.
This comparison is known as temperature-compensated values. Conductivity probes, that have a built-in thermistor, automatically determine the temperature-compensation value. If the temperature is not compensated when taking a conductivity reading, the results will not be reliable. So, always check if your conductivity probe has a thermistor, and if not, use a temperature probe before measuring the conductivity of the water.
A conductivity meter is an essential measuring tool for accurately measuring the conductivity in water. A conductivity meter consists of a conductivity probe/sensor that attaches to the conductivity meter.
Once the probe is inserted into the water, an electrical current flows between the two electrodes inside, reading the electrical current and providing the conductance value.
As previously mentioned, when you measure conductivity in water, it is also important to measure other water quality parameters such as temperature, pH, salinity, and dissolved oxygen.
As high conductivity is linked to the total number of ions in the water, total dissolved solids (TDS) must be removed. Therefore, you can reduce the TDS thus lowering the conductivity via reverse osmosis, distillation, or neutralization using an ion exchanger.
Conductivity increases in water as the number of dissolved solids increases. The conductance level also depends on the ion’s potential to bind with water. Other factors such as water flow and temperature can also cause high conductivity in water.
If you have any questions regarding conductivity or what water testing kits we have to offer, do not hesitate to contact our world-class team at Atlas Scientific.
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