Spores of aerobic spore-forming bacteria were used as microbial surrogates for evaluating drinking water treatment plant performance. A method for assaying for the microbial surrogate was developed. Various water sources were surveyed, and data were collected from coagulation and chlorine inactivation studies. Evaluations for spore removals and turbidity and particle removals were compared for pilot-scale and full-scale water treatment plants. Includes 13 references, tables, figures.