Most tastes and odors in water supplies come from naturally-occurring or manmade organic material contamination. Bacterial decomposition of humic material imparts taste to surface waters. The action of algae and actinomycetes gives rise to objectionable tastes. Chlorination of humic material leads to chlorophenols that are of far stronger odor and more antigonistic to taste than the original phenol and unreacted Chlorine. Most of these odors are removed with Ozone treatment. Even some sulphur compounds such as hydrogen sulfide, mercaptans or organic sulphides can be oxidized to Sulfates with Ozone.