The purpose of this study was to determine how the method of recording inventory accounting system at PDAM Tirta Satria Purwokerto. In this study the author uses two sources of data obtained directly through the interview or interview method and the observation method with practical work reports sources. The results of the study found that the method of accounting records used by PDAM Tirta Satria for installation materials is the perpetual method, while for the inventory of operating goods using the physical method. The method of calculating the cost of goods sold used by PDAM Tirta Satria is the first-in-first-out (FIFO) method. The related functions in the inventory system, starting from the entry of goods to becoming inventory items, are the warehouse section, the finance section, as well as the budget section and reports. The internal control system contained in the inventory accounting system at PDAM Tirta Satria is as follows: Regarding the strict separation of functional functions in the implementation of the stage of purchasing goods to become inventory items, namely the warehouse section and accounting section, there is a system of authority to authorize the implementation of each transaction.