This article discusses pilot plant studies on floc blanket clarification done by the Water Research Association at Medmenham, United Kingdom. British and American practices differ concerning the type of clarifier used; the U.S. uses the horizontal system with preflocculation facilities while in the U.K., the horizontal tank is quickly disappearing in favor of floc blanket clarifiers. These studies make theoretic comparisons and consider reported experience on the use of different designs of tanks.