Extracting Energy from Rain Water

http://en.wikipedia.org/wiki/Hydro-electric_power

http://www.waterhistory.org/histories/waterwheels/

If your rain fall is steady, construct above ground funnel type collectors in multiples, collect the water to a high head erected reservoir, from which you can generate Hydro electricity.

Do some mini model set up test to decide height of funnel collectors, flow rate, tank size, effective Hydraulic head and proceed.

Your idea is to get the Hydraulic head from collection tank to turbine of rain water before reaching earth.