Does Ozonation of Drinking Water Reduce the Risk of Bladder Cancer?

Background

Chlorination is the most widely used method of disinfecting public drinking water, but it reacts with organic matter in the water to form by-products such as trihalomethanes. Earlier research had linked long-term exposure to chlorinated surface water, and its trihalomethane by-products, with an increased risk of bladder cancer. Ozone is an alternative disinfectant that does not generate the same by-products, so researchers set out to establish whether using ozone instead of, or alongside, chlorination altered a population's bladder cancer risk.

Study design

This was a hospital-based case-control study carried out across seven medical centres in France between 1985 and 1987. It compared 281 people diagnosed with bladder cancer against 272 controls without the disease. Researchers used structured interviews to reconstruct each participant's lifetime residential history, the source of their drinking water (surface water versus groundwater), and which disinfection methods - chlorination, ozonation, or both - had been used to treat that water supply over time.

Findings

Bladder cancer risk rose with longer exposure to chlorinated surface water, and this risk increased further among people whose water supply had higher measured levels of trihalomethanes. By contrast, the risk of bladder cancer fell as the duration of exposure to ozonated water increased. The data suggested that ozonation reduced the excess risk otherwise associated with chlorination of surface water, and that ozonation on its own could carry an independent protective association.

What the authors concluded

The authors concluded that ozonation of drinking water appeared to reduce the bladder cancer risk associated with chlorination of surface water, and that ozonation alone could have an independent beneficial effect on bladder cancer risk. They framed this as supporting evidence for considering alternative water disinfection strategies to chlorination, particularly in areas using surface water sources with higher organic content.

Limitations of this study

This was a retrospective case-control study, which relies on participants' recall of decades-old residential and water-source history - a design vulnerable to recall bias and to gaps or errors in reconstructing past exposure. The sample (281 cases, 272 controls) came from hospital populations in one country, France, in the mid-1980s, which may limit how well the findings generalise to other regions, water treatment infrastructures, or time periods. As with any observational study, other bladder cancer risk factors, such as smoking history and occupational chemical exposure, could have influenced results despite statistical adjustment, and an association of this kind cannot on its own establish that ozonation directly causes a reduction in cancer risk.

This study concerns population-level associations between drinking-water disinfection methods and bladder cancer risk in a historical French population - it is not evidence about the therapeutic use of ozone in people who already have cancer. It does not establish ozone as a treatment or cure for cancer itself. Ozone therapy is a complementary approach and should always be discussed with your oncology team.