Testing the electrical conductivity of water provides much practical information about a solution. Not only is the conductivity measurement itself useful, but it can also be used to estimate the total dissolved solids (TDS) or salinity of water. Because conductivity measurements are simple, and fast, they are highly suitable for routine testing and long-term monitoring. Some examples of applications of conductivity measurement are described below.
Natural Waters, Aquaculture and Environmental Applications
In natural waters, conductivity is mainly used to estimate the concentrations of dissolved salts in the water, which in can provide insights into processes affecting the water. In river waters, for example, the conductivity (and TDS) of water may increase in the summer when evapotranspiration is high and decrease when the water is diluted by snowmelt or heavy rains. In coastal areas, the conductivity of water may change with mixing with salt water, and the conductivity of water may rise when it becomes contaminated with road salt in areas with cool climates.
For water resources, the conductivity may indicate whether or not the water is too saline to be drinkable or useable for irrigation or industrial use.
In places where there is potential for water to become polluted, the water may be monitored for changes in conductivity that could indicate contamination from a spill or leak. In ecosystems and aquaculture, aquatic plants and animals have certain ranges of salinity that they can tolerate. Because of this, the conductivity of water bodies such as ponds may be monitored to warn if the salinity is in danger of falling outside of the tolerable range for certain fish species, for example.
Water Treatment and Industrial Applications
Water treatment may be used to make water safe to drink or suitable for industrial use. In many industrial applications, scale (precipitation of mineral deposits) or corrosion may be a concern. Because conductivity can be used to estimate the dissolved mineral content of water, it may be used to monitor demineralization processes used to prevent scale or remineralization processes used to prevent corrosion. Conductivity may also be used to monitor the effectiveness of desalinization, which is another water treatment process that removes salts to make water drinkable or useable for industrial processes.
In other industrial applications, conductivity measurements may be used to detect leaks (such as in heat exchangers), where the leaking water may have a higher conductivity. Conductivity may also be used to monitor the effectiveness of rinsing procedures, where a low conductivity of water in contact with the rinsed object indicates an effective rinse. In special circumstances, such as in ammonia solutions, conductivity can even be used to measure pH with more precision than a typical pH meter due to the strong relationship between conductivity and pH.
Agricultural and Hydroponics Applications
For irrigation, the salinity of water is an important factor. If the salinity is too high, salts will accumulate in soil as the water evaporates, which may degrade soil quality and inhibit plant growth. Water with a conductivity of less than 700 uS/cm is acceptable for unrestricted irrigation use, and the use of water with conductivity values greater than 3000 uS/cm should be severely restricted.
Conductivity can also be used to monitor nutrient concentrations in liquid fertilizers. A quick check of the conductivity of liquid fertilizers can guard against mistakes such as improper mixing or malfunctioning injectors, protecting crops from wasteful over-fertilization or inadequate fertilizer application.
Similar to fertilizer application, conductivity is used in hydroponics to monitor the concentrations of nutrient solutions. If the conductivity gets too high, indicating a nutrient concentration at toxic levels, plants may be harmed or die. Low conductivities can indicate inadequate nutrient supply. Conductivity monitoring can be used as part of automated nutrient supply systems. In addition to monitoring nutrient supply, conductivity measurements can be used to make sure that salt concentrations are in the range tolerated by the plant.
Conductivity measurements are simple and fast, making them very practical for making routine assessments of the salt concentrations of water. Whether assessing the concentrations of salts, contaminants or nutrients, measuring conductivity can reduce the need for more expensive or time-consuming tests. There are many factors that affect conductivity, such as the concentrations and types of dissolved salts present in the water, so knowledge of the chemistry of the system in question is often necessary for interpreting conductivity measurements.
 Abrol, I. P., Yadav, J. S. P., & Massoud, F. I. (1988). Salt-affected soils and their management (No. 39). Food & Agriculture Org.