Kulong formed from tin mining activities has the potential as a source of water. Kulong in Beluluk Village, Pangkalan Baru District, which can be used as a water source is Kulong Krasak. The use of the kulong as a water source is not only seen from the ability of the kulong to meet the water needs of the community but also must maintain its sustainability. The reliability analysis of the kulong is a way to find out the amount of water release that is allowed so that the sustainability of the kulong is maintained. To determine the availability of Kulong Krasak water for the next 16 years, a prediction of water availability is made, namely from 2022 to 2037. From the results of the analysis, it was found that the water demand in Beluluk Village in 2037 was 7.86 l/s. The maximum water availability occurs in April, which is 20.43 l/s and the minimum occurs in September, which is 6.57 l/s. The results of the standard operating rule analysis show that Kulong Krasak has 100% reliability if the release target is 5.61 l/s of the total water demand, which is 7.86 l/s.