Abstract: This invention presents a unique gas/liquid contact chamber that produces intimate contact between a gas, such as ozone, and a liquid in a manner that promotes the greatest possible mass gas transfer of the gas into the liquid. This contact chamber may be coupled with other contaminated water treatment technologies giving contaminated water treatment systems that produce pure water. By the use of combinations of selected technologies specific contaminated water treatment problems, such as disinfection of wastewater treatment plant effluents or portable water treatment systems for emergency use, may be developed. Such water treatment systems also combine the use of fine spray technology, gas/liquid mixing technology, and fine bubble technology for mass gas transfer of gas into liquid. The contact chamber and the systems it can be combined with, are all simple, economical, easily constructed, and highly flexible in application and physical arrangement.