Domestic water demand is analyzed based on the number of population and the standard of water demand in served administrative region. To estimate the water supply, this study used the models of NRECA and F.J. Mock. For analyzing reservoir reliability based on the simulation discharge result of F.J. Mock and NRECA during 20 years there was needed discharge data generated by using Thomas Fiering method. Simulation result of small-dam reliability by carrying out the simulation process every

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... ge data of generated result along 20 years with the projection during 20 years indicated that discharge result of NRECA was failure in 2004 and it assumes that there is no parameter change in catchment, it had the possibility of reliability on 100% in 2007 and 25% in 2026. however, discharge result of F.J. Mock had the possibility of reliability on 100% and it was happened in 2007, and 25% in 2026 for the whole simulation of discharge. There was no discharge data in study location, so minimum discharge was the optional one. Based on the two methods, the Qmin of F.J. Mock has the reliability level of 100% in 2007 until 2026. However Qmin of NRECA has only the ability to serve the whole population (100%) in 2007 but for the next years there was decreasing until 25% in 2026.