Undershot waterwheel at low flow with an average discharge of 0.12 m3/s and 613.2 W water horsepower are used to turn the waterwheel. The rotation results obtained with aluminum material is 24 RPM which has a density of 2.71 g/cm3 while the lowest rotation is owned by a galvanic of 20 RPM with a density of 7.49 g/cm3. From the experiment, it was found that the difference between the materials used was due to the different density. The efficiency of waterwheels with aluminum material has the highest value, namely 30%, while the lowest using acrylic material has an efficiency of 23%. For the highest generator efficiency using aluminum material with an efficiency of 4.2%, the second has an efficiency of 3.6% using Aluminum Composite Panel material. Aluminum has the highest efficiency because it has less density than galvanized. In addition, the thickness of aluminum is also very influential, where aluminum has a thickness of 1.14 mm while Galvanized has 0.98 mm.