A fluid-driven power generating apparatus is a power generator in form pipes with either water wheels or balls with circumferential indents rotating therewithin. The water wheels or the balls are rotated by the fluid flow within the pipes. Each of the water wheels or each the balls has a wheel axle or a ball wheel axle which is encircled by a metal coil. Each metal coil is rotated by the fluid flow within a magnetic field produced by the electromagnetic layer attached to each of the pipes. Through the rotations of the metal coil within the magnetic field, electricity is thus created and stored in an energy storage device. Another variation of the present invention is a closed-system fluid-driven power generating apparatus with mercury as the driving fluid. The present invention can be incorporated into plumbing, dip, sprinkler systems as well as watercrafts such as ships, submarines, jet skis, etc.