Narok Water and Sewerage Services Company (hereinafter, called NARWASSCO) supplies water at Narok town and Ololulung'a town in Kenya. As of February 2019,we have 4,689 water connections and 74,314m3 of water consumption in Narok, also have 580 water connections and 5,736m3 of water consumption in Ololulung'a. Total length of pipeline is 144.2km in Narok and 71.7km in Ololulung'a. NARWASSCO, currently uses FOSS4G to do data collection and data utilization for water supply services. For example, mapping of all water facilities in the company, and the collected data have been used to improve operations (application of new connection, leakage management, meter reading, customer care, etc.). We can say Narok water is the first water company which started to use FOSS4G in Kenya. <br> Our interesting is how water company use GIS inventory data to reduce Non-Revenue Water (NRW). NRW means physical losses(leakage) and commercial losses(meter reading error, illegal connection, etc.). We think GIS technology can contribute a lot of things for water supply services, so we would like to share our experience and get some idea from participants of FOSS4G conference.