The Athens Water Supply & Sewerage Company S.A. (EYDAP) installed the online THM-100™ analyzer to the drinking water reservoir outlet of the Galatsi Water Treatment Plant for a three-month evaluation period, providing EYDAP with continuous online analysis of trihalomethane (THM) values. The real-time THM data helped EYDAP understand how changes in raw source water quality and chlorine contact time affect the total THM (TTHM) concentration and THM speciation composition. With the help of the reliable data provided by the THM-100, EYDAP was able to mitigate better the presence of harmful THMs across the service area.