The physics thingy you're missing is "potential energy." To raise a mass m a height h given the gravity g you need mgh energy. The minimum energy needed to ra

The physics thingy you're missing is "potential energy." To raise a mass m a height h given the gravity g you need mgh energy. The minimum energy needed to raise 1 kg 1000 meters given gravity of 10 m/s/s gravity = 10,000 Joules. It doesn't matter if you raise the water to the top to pour it in at the surface, or send pressurized water out of vents at the bottom of the lake. With the latter, sure, you're putting the water lower down, but that water is pushing other water up and out of the way, so the end result is the same - if you add more water, the water level goes up.