What is Electrical Conductivity in Water?
Electrical Conductivity (EC) refers to the ability of water to conduct electricity.
The conductivity of water is an electrical measure of the amount of inorganic salts
in a solution.
- These include chemical salts and minerals, such as calcium, phosphorus, nitrogen, iron and other ions
- Ions are also known as electrolytes
- The more ions in water, the greater its’ ability to conduct electricity and the higher the conductivity of the water
- Organic compounds do not split into ions and do not affect the EC
- Pure water / distilled water has very low EC because there are no ions
- Salt water has high EC – sea water ± 50 000 ECs
- Sodium, potassium, calcium and magnesium are common ions that affect EC in water
- Ground water that has travelled over porous sedimentary rock or been concentrated in a drought will have a higher EC of 30 – 170 mS / m
- Rain water usually has an EC < 1 mS / m
- Factory wastewater, sewage spills and agricultural waste can also increase EC
Why do we measure Electrical Conductivity in Water?
It is one of the most frequently measured
and useful water quality parameters as it is a fairly constant indication of water quality. It can be an early indicator
of change because of evaporation, pollution or chemical addition, ground water seepage.
What happens when the concentrations of ions in water increase (the EC becomes greater)?
- Salty to taste and upsets the salt balance in our bodies
- Unsafe to drink
- Increased blood pressure in susceptible people
- Cause poor health / death in plants and animals
- There is a correlation between conductivity and salinity. High salinity levels will lower the amount of dissolved oxygen in the water, which affects aquatic organisms
How to Measure Electrical Conductivity in Water
How to choose and Care for the Right Electrical Conductivity (EC) Meter
- EC is measured with a meter (electronic tester) that has an electrode
- EC measurements are affected by temperature, so most good EC meters have built in temperature control (ATC)
- 1 milliSiemen (ms) / cm = 1 000 microSiemens (μS) / cm or ECs
- To convert mS / cm to μS / cm, multiply the reading on the instrument by 1 000
How are Total Dissolved Solids (TDS) and Salinity in Water related to Electrical Conductivity (EC)?
Total Dissolved Solids (TDS)
is a measure of the total inorganic salts (ions) in solution.
Conductivity measures the activity of the ions – their electrical charge. This is much easier to measure than the Total Dissolved Solids, so conductivity (EC) is often used to estimate the TDS concentration.
You can use this equation to estimate the TDS:
Most common solutions:
TDS = 0.65* 1 000 x EC (mS / cm)
High concentration wastewater / saline solutions (EC > 5 000
TDS = 0.735 OR 0.8 * 1 000 x EC (mS / cm)
Alternatively, a multi-parameter meter
can be used, which will provide both measurements.
is a measure of total dissolved salts in water.
Practically, this is often derived from the simpler conductivity measurement, but now there is also a more precise absolute salinity measurement TEOS-10.
Salinity measurements based on conductivity values can be unitless or expressed as Practical Salinity Units (PSU).
Water Quality Regulations in South Africa:
Wastewater General Limits
Electrical Conductivity (mS / m) – 70 mS / m above intake to a maximum of 150 mS / m
Drinking Water (SANS 241:2015):
Conductivity at 25°C (mS / m) – ≤ 170 mS / m
Further Learning in the South African context:
Geographical differences in the relationship between total dissolved solids and electrical conductivity in South African rivers
Establishing a conversion factor between electrical conductivity and total dissolved solids in South African mine waters
River Water Quality in the South African Sugar Industry