Whether we swim for fun, sports, or health, we expect the water to benefit us. Pool water wets our whole body and when swimming we often take it in our mouths. Especially, our children are likely to drink pool water. Chlorination is still the most popular method for swimming pool water disinfection. Although chlorine kills all microorganisms, including viruses, many toxic substances, collectively called disinfection by-products, are produced. Both skin and mouth are the pathways through which these substances enter the body. Chlorine kills not only bacteria contained in the water but also beneficial bacteria that symbiotically reside on our skin. The body releases organic substances into water, which then reacts with chlorine to form disinfection by-products. Many epidemiological studies have linked the effect of chlorine in pool water with respiratory problems and nasal bleeding. A detailed scholarly study by a reputable organization can be found here.