During pilot-plant studies of disinfection by-products (DBPs) other than trihalomethanes (THMs), the authors found that pH is the chemical variable with the most significant effect on DBP formation. It appears that in water treatment, there would have to be a trade-off between control of THMs (low pH) and control of most other DBPs (high pH). The experiments also indicated that precursor control may be similar for all of these DBPs--through physical removal mechanisms. Includes 12 references, tables, figures.