The City of Paso Robles, California, used an online water quality instrument to characterize and monitor low levels of bromodichloromethane (BDCM) and dibromochloromethane (DBCM) in its treated wastewater for groundwater recharge (GWR) use. The high frequency of reliable and accurate trihalomethane (THM) data provided by the online THM instrument proved essential to the City’s disinfection by-product (DBP) strategy to obtain regulatory compliance with NPDES permit levels.