Water conductivity

Conductivity.

Conductivity in water.

Conductivity is the measure of the capacity of water to conduct an electric current. This measure is related to the concentration of ions in the water, their concentrations, mobility and valence, as well as the temperature in which the liquid medium is found (1).

Ions come from dissolved salts and inorganic matter (alkalis, carbonates, chlorides and sulfides). The compounds dissolved in the water are then transformed into ions that can also be referred to as electrolytes. The higher the concentration of electrolytes in the water, the higher its conductivity (or electrolyte conductivity). Some of the electrolytes that can be found in water are Ca2+, Mg2+, Na+, K+, HCO3, SO42-.

Ions conduct electricity due to their positive and negative charges (cations and anions). Regardless of the number of anions and cations in the water, the electrical conductivity always remains neutral.

By determining the concentration of dissolved ions in the water (electrolytes), the amount of total dissolved solids (TDS) in the water can be determined.

How do you measure conductivity in water?

The units in which water conductivity is measured and reported commercially are the microsiemens per centimeter (μS / cm). The μS is equivalent to siemens (S), and the S is equal to a mho (℧). This is because, the electrolytic conductivity is defined as the inverse of the electrical resistance (reported in ohms Ω) (2).

Conductivity is measured with equipment that has an electronic probe that applies a voltage between two electrodes. The voltage drop is used to measure the resistance of the water that is changed by conductivity.

Why is water conductivity important?

Water conductivity works as one of the most common parameters for determining water quality. Being an accessible, easy and useful method, water conductivity is a measure used in industrial plants, treatment plants, and can also be for domestic use.

In order to have a water quality monitoring, conductivity is measured in pipes, channels, streams, lakes, etc. In industry, conductivity is measured at various points where water flows, to keep track of water used in processes, services or waste.

How are TDS related to electrolyte conductivity?

Because these two terms are related and directly proportional, it means that the higher the conductivity, the higher the concentration of TDS. It is easier to make a conductivity measurement and have a TDS result in the water. Currently, there are measuring devices that by means of the electrical conductivity of the water (or solution), calculate the amount of TDS in ppm (mg / L).

What is the water conductivity levels?

It depends on the areas where the water is located and flows, these are the levels of electrolytic conductivity that could be reported. Below is a table from State Water Resources Control Bord (3) showing some examples of conductivity in water.

Water type

Conductivity (μS / cm)

Distilled water

0.5 – 3.0

Melted snow

2 – 42

Drinking water in the U.S.A.

30 – 1500

Irrigation supply water

<750

Hardness can also be expressed through conductivity, since this method can be applied as salts. The following table is an example of the relationship between the concentration of sodium chloride in water and the conductivity of the same at a temperature of 25 ° C (4).

 

Conc. NaCl (g / L) %
Conductivity (μS / cm)
Conc. NaCl (g / L) %
Conductivity (μS / cm)
1.0
2.0
11.0
19.2
2.0
3.9
12.0
20.8
3.0
5.7
13.0
22.4
4.0
7.5
14.0
24.0
5.0
9.2
15.0
25.6
6.0
10.9
16.0
27.1
7.0
12.6
17.0
28.6
8.0
14.3
18.0
30.1
9.0
16.0
19.0
31.6
10.0
17.6
20.0
33.0

 


Sources

  1. American Public Heatlh Association. Standar Methods for the Examination of Water and Wastewater. Washington, DC : American Water Works Association; Water Environment Federation, 2017. 55-1979.
  2. Fondriest Environmental, Inc. “Conductivity, Salinity and Total Dissolved Solids.” Fundamentals of Environmental Measurements. [Online] March 13, 2014. https://www.fondriest.com/environmental-measurements/parameters/water-quality/conductivity-salinity-tds/.
  3. State Water Resources Control Bord . Information Booklet Electrical Conductivity/Salinity. [Online] The State Water Board. https://www.waterboards.ca.gov/water_issues/programs/swamp/docs/cwt/guidance/3130sp.pdf.
  4. IEEE Journal of Oceanic Engineering. Salinity (density of salt in water) and conductivity. Piscataway : JOE Editorial Board, 1980. 0364-9059.
  5. Infoagro. "¿Qué es la conductividad eléctrica y los sólidos totales disueltos?" [Online] Infoagro, November 29, 2017. https://mexico.infoagro.com/que-es-la-conductividad-electrica-y-los-solidos-totales-disueltos/.

Last updated 17/02/2020.

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