Abstract: Process for treating, especially waters to be made drinkable, with ozone in a reactor (2), especially with a bubble column, in which ozone is generated (in 1) in a gas enriched in oxygen containing at least 70% of oxygen by volume, to produce an ozonised gas containing more than 2%, especially from 2% to 20%, of ozone by weight, in which the said ozonised gas is diluted by means of a secondary fluid and the treatment is carried out by means of the diluted ozonised gas.Another subject of the invention is a plant for the use of the process according to the invention, comprising an ozoniser (1) generating an ozonised gas, at least one reactor (2) for treatment with ozone, and a supply pipe (3) connecting the outlet of the ozoniser with the inlet of the reactor, in which means (4, 5; 15, 16), for injecting a secondary fluid into the said supply pipe (3), are additionally provided.