Final answer:
The first hydro-powered mills were built along rivers to grind grains such as wheat.
Step-by-step explanation:
The first hydro-powered mills, also known as water mills, were built along rivers to take advantage of the kinetic energy of the moving water. These mills were primarily used to grind grains such as wheat. The force of the water was used to turn the millstones, which would crush the grains into flour. They did not produce electricity as electricity was not yet harnessed during that time.
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