The theoretically power available from falling water can be expressed as

P_th = ρ q g h                      (1)

where

P_th = power theoretically available (W)

ρ = density (kg/m³) (~ 1000 kg/m³ for water)

q = water flow (m³/s)

g = acceleration of gravity (9.81 m/s²)

h = falling height, head (m)

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