Abstract: A water purification system having a pre-filter, a series of germicidal radiation chamber filter units alternating with a series of mechanical filter units and having a flow measuring device affixed to the output part of a final mechanical filtering unit. The rate of flow through the series of alternating germicidal and mechanical filtering units being measured by the flow measuring device and in turn controlled by an electrically operated valve so as to keep the rate of flow, of water being purified, through the series of alternating germicidal and mechanical filters at some predetermined and optimal setting with respect to the efficaciousness of the germicidal filters.