A clean water supply system in principle must be planned and built so that in its construction it can meet the objectives including: the availability of water in sufficient quantities with quality that meets the requirements of drinking water, the availability of water in a sustainable manner, the availability of water at affordable prices by the community as consumers. PERUMDAM Tirta Satria Purwokerto Branch I as a clean water provider service has served 5 sub-districts, Baturaden District, North Purwokerto District, East Purwokerto District, South Purwokerto District, and West Purwokerto District. This study aims to determine the clean water needs of customers in the PERUMDAM Tirta Satria Branch I Purwokerto area and review the availability of existing water sources. From the results of the study, clean water needs based on the number of customers for South Purwokerto sub-district 72,49 lps, West Purwokerto sub-district 73,07 lps, East Purwokerto sub-district 115,01 lps, North Purwokerto sub-district 70,23 lps, and Baturaden sub-district 9,50 lps. The total clean water requirement is 340,3 lps. The total clean water production is currently 4,499.12 lps. From comparison, the current availability of clean water can meet the needs of clean water until 2031. The reservoir capacity required in 2031 is 7056,5 mɜ while the total capacity is currently 3000 mɜ so additional volume is needed to the reservoir capacity.