When ozone is injected into water, it will quickly react with any organics in the water. The objective of ozone treatment is to achieve a residual concentration high enough to continue to oxidize organics as the water passes through the distribution system, but not so high that adverse effects are seen. In this post, we will walk you through how to calculate residual ozone concentration for your specific application! Stay tuned!

It is important to understand the fundamental mechanisms involved with how to compensate for the half-life of ozone in your water treatments.

This information is highly recommended to assist ozone water treatment specialists in calculating residual ozone for water treatment applications.

O3 Half-Life Time as a Function of Temperature:

Dissolved In Water (pH 7): Half-life time at Temp

~ 30 minutes 15 ºC

~ 20 minutes 20 ºC

~ 15 minutes 25 ºC

~ 12 minutes 30 ºC

~ 8 minutes 35 ºC

When the half-life of ozone at 30C is 12 minutes, that indicates that there will be 50% less ozone in the water if we injected the gas instantly.

However, we continue to inject ozone into the water in actuality, and we maintain the concentration at a high level.

As a result, we must saturate the pool with enough ozone so that it can compensate for the half-life of ozone destruction and maintain a constant desired residual ozone concentration in the water.

Pool Water Example

Let’s use the preceding data to illustrate how it might be utilized. Let’s say we need to keep a pool water concentration of 0.1 parts per million (ppm).

We know that 1ppm=1 g/m3

The 10 g of ozone dissolved in 100 m3 of water will result in a concentration of 10 g.(100 m3 x 0.1 g/m3 = 10 g)

We also know that 12 minutes = 0.2 hour (12 min/60 min=0.2h)

It’s easy to see why each 12 minutes, 10 grams of ozone dissolves in the water and becomes a 5 g, 2.5 g, 1.25 g…, and so on. To make up for it, we will have to inject more ozone.

Dividing the amount of ozone required by half-life of water to determine the amount of dioxide required to be injected every hour to counteract it.

We suggest the following formula: O3 n/HL=O3 c


O3 n – Ozone gas is generated naturally in the atmosphere. Ozone destroys itself at a faster rate than other gases, requiring more to be created for each pound of pollutants destroyed.

HL – According to the water temperature listed above, the half-life of ozone is approximately three hours.

O3 c – The actual amount of ozone required to be injected in order to maintain residual concentration at the natural water temperature when correcting for thermal effects.