The objectives of the research discussed in this paper were to determine how to chemically pretreat low turbidity water for efficient rapid rate filtration, to determine the effect of process variables on the removal of Giardia cysts, turbidity, and bacteria, and to ascertain whether use of a surrogate indicator is feasible for assessing the efficiency of treatment for removing Giardia cysts. The process variables included chemical pretreatment (coagulant selection and dosage), filtration mode (conventional, direct, or in-line), filter media, hydraulic loading rate, and temperature. An ancillary objective was to determine the removal efficiency of rapid rate filtration when coagulation chemicals are not used. Research results indicate that proper chemical pretreatment is imperative if the rapid rate filtration process is to be effective for low turbidity waters. Selection of the proper coagulant aid polymers to use with the primary coagulant is most important, as is the use of proper dosages to achieve high reductions of turbidity. With proper chemical pretreatment, removals can be expected to exceed 70 percent for turbidity, 99 percent for bacteria, and 95 percent for Giardia cysts. With no chemical pretreatment, removals of Giardia cysts, bacteria, and turbidity can be expected to be in the range of 0 to 70 percent. Other process variables were not as important as chemical pretreatment. Analysis of the data by means of histograms showed that either percent removal of turbidity or percent removal of total coliform bacteria could serve as a surrogate indicator of percent removal of Giardia cysts. Includes 9 references, tables, figures.