Abstract: A method and apparatus for the purification of water with ozone and ultraviolet radiation. Oxygen-containing gas, such as air, is directed to flow in a confined path past an untraviolet radiation source, such as a mercury vapor lamp. The absorption of ultraviolet radiation by oxygen produces ozone which is entrained in the flowing gas. The gas is next mixed with the contaminated water and the mixture of water and ozone is then directed past the same ultraviolet source in a path isolated from the confined path of gas alone. The ozone in the water acts directly to kill bacteria and viruses and to oxidize undersirable compounds in the water. The ultraviolet radiation also acts directly to kill bacteria and viruses in the water. Additionally the ultraviolet radiation acts as a catalyst for the disinfecting and oxidizing action of the ozone, so that water purification occurs much faster than would occur if the ozone were acting alone.