Idea of today

Anyone ever thought of using water falling from the sky,
i.e. rain as a source of electrical power?
1. Collect them;
2. Pass through a tunnel;
3. The channel has Generator built-it to convert gravitational potential energy into electricity,

(Added today: 4. We could use filtration mechanism to clean the water for drinking. )

The design of 1 and 2 could be as trivial as this design. Water from sky is lead to the tunnel with spiral trajectory or any design like those. The outer arm of Rotor of the Generator inside the tunnel is lead to rotate against the Stator, which the Generator itself is insulated from water. The electrical energy produce could be stored using car battery.