Gradual changes and improvements in the coagulation and chlorination processes at many water treatment plants have altered the role of the filtration process to such a degree that a review of the function and design of the filter is called for. As a part of this review the Sanitary Engineering Center has cooperated with various State Health Departments and water plants to collect data on the influence of higher rates of filtration on the quality of finished water. This report covers a project carried out in a 3-mgd water plant at Gaffney, South Carolina, from 1959 to 1961. The results emphasize the fact that, when a coarse anthracite filter media is used adequate coagulation is essential to obtain clear water regardless of filter rates. When the coagulation process functioned properly, well-clarified water was obtained at a filtration rate between 1 to 6 gpm per square foot.