Can electricity be produced from running water by the use of dc motors? For example rainwater collected from from the roof of a very tall house say 15m high is directed through a pipe and at it's exit, makes the wheels of a dc motor turn.
If it's a very simple motor then it may be possible just to run it backwards to generate electricity. If it's got electronic controls, probably not.
But is it worth it? Do a quick calculation of the amount of energy available. How much water are you expecting to fall? (roof area x annual rainfall). One cubic metre of water weights 1000 kg.
Height (metres) x mass (kg) x 10 will give you the energy in joules - the total it would be theoretically possible to harvest if you could achieve 100% efficiency.
There are 3.6 million joules in one kWh (one unit of electricity on your bill).
There's just not going to be that much energy to collect.