The water treatment plant (IPAM) in Kampung Damai is one of nine water treatment plants owned by PDAM Tirta Manggar, Balikpapan City. In carrying out clean water treatment, IPAM Kp Damai requires water purification raw materials in alum, lime, and chlorine. Companies often experience shortages or accumulation of raw materials from the rest of the previous production, so that it has an impact on inventory and storage costs. Therefore, we need planning and control of raw materials to optimize the total cost of inventory. The method used in this study is the lot technique in material requirements planning, namely lot for lot and periodic order quantity. The type of data used is primary data and secondary data where the research was conducted. The data collection technique used is secondary data (historical data).The analysis technique used is plotting past demand data, forecasting, and material requirements planning.From the results of the study, it can be concluded that the application of the lot for lot method for each raw material for water purification at IPAM Kp. Damai PDAM Kota Balikpapan can minimize the total cost of inventory compared to the periodic order quantity method.