This research intends to obtain the discharge modeling for supporting water balance in the Konto Hulu sub-watershed-Indonesia, Based on the water balance, it can be investigated the water supply as well as the water demand. The methodology consist of discharge modeling by using F.J. Mock method that is based on rainfall data and some others one. The observed discharge data from the Automatic Water Level Recorder is used as the control of model validation. The potency of water supply is known from the dependable discharge due to the probability of 80% and the results is 22.41 m3/s that is proportional with 706.622 million m3 per-year, The water demand in incoming 25 years on scenario-1 (based on the growth rate) is 95.085 million m3 per-year, however on scenario-2 (based on the increasing estimation of domestic, non-domestic, and industry) is about 93.418 million m3 per-year. The result of water balance shows that the potency of water supply can fulfill the whole water demand or it shows the condition of water surplus reaches until 25% in 2017-2042