A general procedure is suggested for evaluating performance of water filtration plants. Plant operating records should be reviewed. Plant hydraulics should be evaluated. Chemical feed pumps, measuring, and additional points, plus control of chemical doses, are discussed. Rapid mixing and flocculation equipment, energy input, short circuiting and detention time are important. Hydraulics of settling basins should be reviewed. Various aspects of filters, including bed design, hydraulics, backwashing and monitoring, are key factors. Finally, for disinfection to be effective, adequate contact time in the clear well should be assured by baffles.