What does the redox value of water mean?

What does the redox value of water mean?

This value is often used when it considers water treatment, but what does it mean? Redox stands for Reduction and Oxidation potential, another term is the ORP, which stands for Oxidation-Reduction Potential. We now know what it stand for, but what does it mean? It’s hard to explain, but the most important thing it tells us in the world of ozone is the purity of the water and its potential to break down pollution. It is measured in mV and varies from -2000mV to +2000mV. A negative value is practically only used in certain methods to purify water. This page focuses on redox related to ozone (oxidation) so we’ll just focus on positive redox values.

The redox value is measured by a redox sensor which measures the oxidising potential of the water. It also gives you an indication of the amount of dissolved oxygen in the water. Water that’s heavily polluted contains less oxygen because organic pollution consumes oxygen. This is why the redox potential of polluted water is lower than that of clean water.

Redox value and its applications.

Redox value (mV) application
0-150 Some methods for biological purification
150-300 Ponds, fish farms and aquariums
300-400 Cooling towers
400-500 Pools
500-600 Hot tubs and spa’s
600-800 Water disinfection
>800 Water sterilisation
Redox waarde

Redox meter







The redox value also gives an indication of the bacteriological activities of the water.

Below, you’ll see an indication of the relation between redox and the amount of coliform bacteria.

Redox value (mV) Coliform amount per 100ml water
200 300
300 30
400 3
600 0





The redox value is a good indicator of the amount of dissolved ozone in clean water, provided there are no other oxidisers present.

© Tol Watertechniek