This paper describes new regulations governing disinfection and potential operation or engineering responses to acheive compliance, and attempts to clarify appropriate responses to the regulations using a decision tree format. Regulatory information for this paper was drawn from the Federal Advisory Committee's Agreement In Principle (FACA Agreement) and the Notice of Data Availability (NODA) published by US EPA in November, 1997. The technical issues discussed in this paper are based on the assumption that US EPA will promulgate regulations based on the 1997 NODA and FACA Agreement.