Abstract: A system minimizing inorganic and organic contaminants in water circulating in a water system comprises a flow-through filter vessel containing a filter medium and whose outlet is connected by a conduit to a flow-through radiation chamber containing a source of ultraviolet light. An electrostatic probe is inserted into the conduit between the filter vessel and the radiation chamber to subject the water flowing through the conduit to an intense electrostatic field. The filter vessel, conduit and chamber are connected in series to a pump and water utilization apparatus such as a cooling tower, pool or the like so that the water circulates through the filter and the electrostatic field before it enters the radiation chamber to maximize the effectiveness of the radiation chamber in killing organic contaminants entrained in the water.