By identifying weaknesses and optimizing treatment, Pennsylvania has greatly improved performance at its surface water plants. Pennsylvania's Department of Environmental Protection (DEP) initiated a statewide filter plant performance evaluation (FPPE) program for safe drinking water and completed 506 FPPEs at 290 surface water treatment plants. Only 39 percent of the plants were rated “acceptable” for performance at the program's inception in 1988, but by 1996 the percentage had increased to 91 percent—demonstrating that assistance to these systems could lead to successful improvements and decreased risks from waterborne protozoa. The percentage of positive Cryptosporidium (presumptive) samples of the finished water dropped from 35 percent in 1990 to <5 percent in 1996. Positive Cryptosporidium samples have remained below 5 percent in the last five years. The 90th percentile of particle count data showed a postfiltration count of 50/mL in the 3‐ to 18‐μm size range as the threshold for acceptable performance. Because optimized performance is a goal of the FPPE program, the concentrations of 3‐ to 18‐μm particles should remain below 10/mL to minimize breakthrough of pathogenic protozoa. The DEP considers turbidity of <0.1 ntu from each filter as a more optimum level of filter plant performance.

Since 1988, the Pennsylvania Department of Environmental Protection has conducted detailed evaluations of the state's surface water treatment plants. The ongoing program, called Filter Plant Performance Evaluation, is a method of determining the effectiveness of a water treatment plant in removing pathogens and pathogen‐sized particles from the incoming raw water. The evaluation process combines an onsite survey of filter plant operations and general physical conditions. Although the FPPE program evaluations capture a ‘snapshot’ of filter plant performance, they also entail a review of turbidity monitoring records to gain a long‐term picture. This article discusses this program, typical questions asked during filter plant performance evaluations, common problems in treatment, and evaluation tools of the future.