In Indonesia, 2,519 villages do not have access to electricity. This is because its location is difficult to access. Utilizing small-scale hydropower by using the pico hydro type Archimedes turbine could be an alternative solution. The Archimedes turbine operates under low head conditions with a wide range of water discharge. The aims of this study are to determine the value of the critical slope angle (a) that causes overflow leakage, and to observe the effects of turbine slope angle variation on turbine efficiency. This study is composed of an analytical methodology, followed by an experiment. The results from both methods reveal significant differences. The analytical calculation predicted that overflow leakage would drastically reduce turbine efficiency. However, the experiment found that overflow leakage does not significantly decrease turbine efficiency. This result implies that the predicted effects of overflow leakage phenomenon outlined within the analytical methodology of this study is inaccurate. Moreover, this result suggests that determining the critical value of a to prevent overflow leakage is unnecessary.