Electrical conductivity, or EC value for short (from the English term “electrical conductivity”), is one of the most important parameters in water analysis. It indicates how well a liquid can conduct an electric current, thereby providing valuable information about the substances dissolved in it.
In this article, you will learn what factors influence conductivity, how it is measured, how calibration works, and what typical values can be expected in various applications.
What is electrical conductivity?
Electrical conductivity describes a liquid’s ability to conduct an electric current. In aqueous solutions, this ability depends directly on the ions dissolved in them: the more ions present, the better the liquid conducts electricity and the higher the EC value [1].
Pure distilled water contains very few ions and therefore conducts electricity very poorly. As soon as salts, minerals, or other ionic compounds are dissolved in it, its conductivity increases measurably.
Conductivity is typically expressed in microsiemens per centimeter (µS/cm) or millisiemens per centimeter (mS/cm). For very pure water, the unit megaohm-centimeter (MΩ·cm) is sometimes used; this describes electrical resistance and is inversely proportional to conductivity.
The EC value is closely related to the TDS value (Total Dissolved Solids), which is the total amount of dissolved solids. Many conductivity meters calculate the TDS value directly from the measured conductivity using a fixed conversion factor.
Learn more: What is TDS?
What factors affect the conductivity of a solution?
There are three main factors that determine the EC value of a solution:
1. Ion concentration
The more ions there are in a solution, the higher the conductivity. An electrolyte consists of dissolved ions such as sodium (Na+) and chloride (Cl-), which carry electrical charges and can move through the water. More dissolved ions mean more charge carriers and thus higher conductivity [1].
2. Type of ions
Not all ions conduct electricity equally well. Hydrogen ions (H+) and hydroxide ions (OH-) are particularly mobile charge carriers and increase conductivity more than other ions at the same concentration. Larger, heavier ions move more slowly through water and contribute less to conductivity [2].
3. Temperature
As temperature rises, conductivity increases because ions move more quickly through the water at higher temperatures. This effect is typically about 2 percent per degree Celsius [1]. For this reason, high-quality conductivity meters feature automatic temperature compensation (ATC), which converts all measured values to a reference temperature of 25 °C, thereby providing comparable results.
How is conductivity measured?
Conductivity is measured using a probe that is immersed in the sample. The probe contains two or more electrodes, between which an alternating voltage is applied. The meter detects the current flowing through the probe and uses this to calculate the solution’s conductivity [1].
Modern conductivity meters display the value directly in temperature-compensated units of µS/cm or mS/cm.
The measurement process is straightforward:
Step 1: Calibrate the device
Before taking a measurement, the device should be calibrated using a suitable calibration solution. See the next section for more information.
Step 2: Prepare the probe
Rinse the probe with distilled water and gently pat to remove any residue.
Step 3: Measurement
Immerse the probe completely in the sample. Make sure the electrodes are fully wetted and that no air bubbles are trapped between them. Gently swirling the probe will help you obtain a stable reading more quickly.
Step 4: Read the value
The result should only be read once the device displays a stable value. For devices with ATC, the temperature-compensated value is displayed automatically.
Step 5: Clean the probe
After taking the measurement, rinse the probe again with distilled water.
Overview of all Apera conductivity meters
Calibration of a Conductivity Meter
To ensure accurate measurement results, a conductivity meter should be calibrated regularly. Calibration is performed using potassium chloride (KCl) solutions of known concentration, whose conductivity values are precisely defined [1].
A commonly used standard is a 0.01 mol/L KCl solution, which has a conductivity of 1412 µS/cm at 25 °C [1]. For optimal accuracy, the calibration standard should be as close as possible to the expected measurement range.
For measurements over a wide range, we recommend a multipoint calibration using two to five standards of varying concentrations [1]. Many Apera devices automatically detect the standard solution and perform the calibration accordingly.
About Apera’s conductivity calibration solutions
Typical conductivity values in practice
The EC value varies considerably depending on the application. Here are some guidelines [1][2]:
| Water / Usage | Typical EC value |
|---|---|
| Distilled water | < 1 µS/cm |
| Rainwater | 2 to 100 µS/cm |
| Drinking water | 50 to 500 µS/cm |
| Hydroponics | 800 to 2,500 µS/cm |
| Seawater | 45 to 55 mS/cm |
| Industrial wastewater | varying widely |
In hydroponics, the EC value is a direct measure of the nutrient content of the nutrient solution. A value that is too low indicates a nutrient deficiency, while a value that is too high can damage the roots.
In water treatment and drinking water analysis, the EC value provides information about the degree of mineralization in the water and can indicate the presence of contaminants.
In aquaculture, electrical conductivity is an important parameter for monitoring water quality, especially when considered in conjunction with pH and Dissolved Oxygen levels.
Conductivity and salinity
In saltwater applications such as aquaculture or seawater analysis, conductivity is often used to calculate salinity. The relationship between conductivity and salinity is well documented and forms the basis of the Practical Salinity Scale (PSS-78) [3].
Many Apera devices calculate salinity and TDS levels directly from the measured conductivity and display all values simultaneously.
More on this: What is salinity?
Conclusion
Conductivity measurement is a fast, reliable method for obtaining important information about the ion content of a liquid. With the right equipment, regular calibration, and consideration of the effect of temperature, stable and comparable measurement results can be achieved.
Overview of all Apera conductivity meters
Frequently Asked Questions About Conductivity Measurement
What exactly does a conductivity meter measure?
It measures a liquid’s ability to conduct electricity. This depends directly on the number and type of dissolved ions and is expressed in µS/cm or mS/cm.
Why does temperature affect electrical conductivity?
At higher temperatures, ions move more quickly through the water, which increases conductivity. The effect is approximately 2 percent per degree Celsius. Devices with automatic temperature compensation (ATC) convert all values to 25 °C to ensure that measurements remain comparable.
How often should a conductivity meter be calibrated?
If used regularly, it is recommended to calibrate the device before each series of measurements or at least once a day. If used infrequently, calibrate it before each measurement session.
What is the difference between EC and TDS?
EC measures electrical conductivity directly. TDS describes the total amount of dissolved solids and is calculated from the EC value using a conversion factor. The two values are closely related but are not identical.
What calibration solution do I need?
For most applications, a 0.01 mol/L KCl solution with a conductivity of 1412 µS/cm at 25 °C is a good standard. For very high or very low conductivity ranges, solutions that are closer to the expected measurement range are recommended.
Can I measure conductivity and pH at the same time?
Yes, many Apera devices measure both parameters simultaneously, which is particularly useful in hydroponics, aquaculture, and water treatment.
References
[1] American Public Health Association (APHA) (2005) Standard methods for examination of water and wastewater, 21st edn. APHA, AWWA, WPCF, Washington.
[2] Haynes, W. M. (2009). CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data. Boca Raton: CRC Press.
[3] Parkhurst, D.L., and Appelo, C.A.J. (2013), Description of input and examples for PHREEQC version 3–A computer program for speciation, batch- reaction, one-dimensional transport, and inverse geochemical calculations: U.S. Geological Survey Techniques and Methods, book 6, chap. A43, 497 p.