Modifications in water treatment processes or in their sequential placement to optimize reductions in disinfection by-product formation must be cautiously evaluated and monitored for their impact on microbial barriers. Four major treatment concepts were investigated either in pilot plant or full scale: (1) changing the point of application for free chlorine disinfection, (2) applying granular activated carbon (GAC) adsorption for organic removal, (3) ozonation and biological activated carbon (BAC) for increased organic conversions and (4) selection of alternative disinfectants. In the trade-off to minimize trihalomethane production, however, some migration deeper into the treatment train will occur as a result of fluctuating qualities in many surface source waters. None of these issues are beyond control using reasonable treatment precautions by water plant operators. What is needed is a revised monitoring program for water treatment practices that will provide more useful information to fine tune treatment effectiveness.