Unlike Europe, in the United States Chlorine has traditionally been the most accepted swimming pool sanitizer. However, credible research suggests that Chlorine has serious health issues when used in standard recommended quantities as a swimming pool sanitizer.
Chlorine combines with organic load created by human use (sweat, urine, etc.) of the pool and the environment (pollens, airborne debris, etc.) resulting in Chloramines and Trihalomethanes. Research and health agencies have produced evidence that Chloramines and Trihalomethanes may be carcinogenic and could be linked to different cancers. There is also credible research that may link Chlorine/Chloramines off-gas effects at surface level of swimming pools to Childhood Asthma.
A quick history lesson tells us that chlorine gas was responsible for killing several hundreds of thousand soldiers in World War I. Why then in the United States, does Chlorine remain the dominant sanitizer in swimming pools and why is it that pool professionals do not promote proven, healthier sanitation solutions?
Several facts come to mind:
One fact is that human nature is to “stay in your comfort zone”. Many pool companies have been accustomed to Chlorine as a sanitizer for many years and they feel comfortable with what they know.

Another common reason is that some pool companies which rely upon chemical sales as a source of revenue do not wish to provide solutions which drastically reduce chemical revenues.
An important explanation may be lack of knowledge or training on alternative solutions to Chlorine as a solution to overall pool maintenance. Ozone generator companies share some of the responsibility for this because they have not educated pool owners sufficiently enough to create a need for dealers and builders to learn more about the benefits of Ozone.