We live in a rural area and our well water comes from storage tanks that are continously being ozonated before passing through an infra red lamp.

The water in the house smells like it contains chlorine and so does the water in the storage tank upon climbing to the top cover and smelling.

There is no source of chlorine and want to know if the ozone can be the source of the bleach odor.

  • $\begingroup$ Do you also have water softener? $\endgroup$
    – MaxW
    Nov 2, 2016 at 1:13

1 Answer 1


Although the primary products of chloride oxidation resulting from the ozonation of saline waters are chlorate salts ("Photochemical oxidation of chloride ion by ozone in acid aqueous solution", Environ Sci Pollut Res (2015) 22:16554 – 16569), a portion of the chloride is also known to oxidized to molecular chlorine, $\ce{Cl2}$.

Human olfactory senses can detect $\ce{Cl2}$ at levels as low as 0.2 ppm in air. This World Health Organization publication reports that some non-seawater contaminated surface waters in the UK contain greater than 40 mg/L chloride, and some seawater-contaminated aquifers used for drinking water in both the US and Philippines contain chloride concentrations on the order of a few hundred mg/L.

The degree of oxidation of $\ce{Cl-}$ to $\ce{Cl2}$ by ozone depends on several factors including temperature, lighting conditions, pH of the well water in question, and of course chloride concentration. However, based on the information given above, low-percent level conversion rates of $\ce{Cl-}$ to $\ce{Cl2}$ by ozone oxidation should be feasible, which under the right conditions, would result in the production of a noticeable chlorine odor. It indeed seems that $\ce{Cl-}$ to $\ce{Cl2}$ conversion represent the most likely scenario for the chlorine odor detected from the treated well water.

NOTE: OP mentioned an "infra red lamp" as part of the disinfectant process for the drinking water. I suspect this really meant, or was in addition to, a UV lamp, which would further promote the oxidation of chloride per my first reference.


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