AMS will be at the AWWA Conference, where Sharon Fillman of United Water will be presenting a paper on Wednesday 7th entitled ‘Using an on-line THM Analyser to aid in Compliance with DBP Regulations’. The US EPA Stage 2 DBP Rule requires public water systems (PWSs) to further evaluate their ability to maintain compliance with TTHMs at individual compliance sample locations within the distribution systems. The Stage 2 Rule imposes a locational running annual average, LRAA, at each sample site which differs from the Stage 1 DBP distribution quarterly average, QRAA, of all sample sites. United Water Pennsylvania’s (UWPA) Harrisburg system has been gearing up for Stage 2, by altering coagulation, flocculation, sedimentation, filtration and disinfection processes for several years. UWPA has experienced a reduction in TTHMs and increased operating costs as a result. Despite these changes, UWPA’s Harrisburg system continues to be challenged with TTHM compliance. To be more proactive at maintaining compliance, UWPA leased an automated, online TTHM analyzer from Aqua Metrology Systems (AMS), to provide a process optimization tool to adjust the treatment process under varying source water conditions. The AMS TTHM analyzer provided six finished water TTHM concentrations daily at 4 hour increments. This online TTHM analyzer data was compared with UWPA’s statistical regression analysis, currently used to estimate TTHM concentration in the finished water, and with results from three local commercial laboratories. Results show that the AMS THM100 analyzer provides real time TTHM levels in response to changes in source water quality and can be used as an operational tool to aid in DBP compliance.