Evaluating the Electrical Conductivity of Water

The electrical conductivity (EC) of water estimates the total amount of solids dissolved in the water (the water’s total dissolved solids, or TDS). TDS is measured in ppm (parts per million or milligrams per liter).

What are the Affects EC of Water?

EC of the water depends on the water’s temperature: the higher the temperature, the higher the electrical conductivity is going to be.

The electrical conductivity of water increases 2 to 3% for every 34°F increase in water temperature.

Many EC meters nowadays automatically standardize readings to 77°F. While EC is a good indicator of total salinity, it does not provide any information about ion composition in water.

The same EC values can be measured in low-quality water (water rich with sodium, boron and fluorides) as well as in high-quality irrigation water (adequately fertilized water with appropriate nutrient concentrations and ratios).

Units of EC Measurement

The commonly used units for measuring EC of water are:

μS/cm (microSiemens/cm) or dS/m (deciSiemens/m), where 1,000 μs/cm = 1 dS/m

TDS vs. EC

Since EC is a measure of the capacity of water to conduct electrical current, it is directly related to the concentration of salts dissolved in water, and therefore to the TDS.

Salts dissolve into positively and negatively charged ions, which conduct electricity. Since it is difficult to measure TDS in the field, it is the EC of the water that is used as a measure.

EC of water can be determined in a quick and inexpensive way using portable meters. Distilled water does not contain dissolved salts and, as a result, it does not conduct electricity.

It has an EC of zero. Nevertheless, when salt concentrations reach a certain level, EC is no longer directly related to salt concentration.

This is because ion pairs are formed. Ion pairs weaken each other’s charge, so above a certain level, higher TDS will not result in equally higher EC.

EC can be converted to TDS using the following calculation: TDS (ppm) = 0.64 X EC (μS/cm) = 640 X EC (dS/m). This relation provides an estimate only.

How Does EC Affect Plant Growth?

The EC of water is actually a measure of salinity. Excessively high salinity can affect plants in the following ways:

• Specific toxicity of a particular ion (such as sodium)
• The higher osmotic pressure around the roots prevents efficient water absorption by the plant

Some plants are more susceptible to EC than others, and each species has its own electrical conductivity threshold. Surpass this threshold and yields begin to decrease.

Using EC Portable Meters

Most EC meters have the following information indicated on them or in their manuals:

• The measurement units it uses. Different EC meters may use different units, such as ds/m or μs/cm
• The range of the measurement
• Whether the instrument automatically compensates for temperature. If it does not, the measurement of the water EC should be taken at 77°F

How to Take an EC Reading Correctly

• Immerse the EC meter in the water sample. The EC meter should be immersed only up to the level indicated in the instructions. Never immerse the EC meter totally
• Slightly stir the sample water with the EC meter
• Wait a few seconds until the reading stabilizes and take the reading

Now that you know how easy and how important it is to keep an eye on your garden’s EC levels, you’ll be able to reverse toxicities and grow better-tasting crops.