Rain energy?

http://dsc.discovery.com/news/2008/02/07/raindrops-energy.html

Discovery.com scientists have
found a way to extract [0]energy from rain. A new technique could utilize
piezoelectric principles of a special kind of plastic to generate power
from falling water in rainstorms or even commercial air conditioners.
"The method relies on a plastic called PVDF (for polyvinylidene
difluoride), which is used in a range of products from pipes, films, and
wire insulators to high-end paints for metal. PVDF has the unusual
property of piezoelectricity, which means it can produce a charge when
it's mechanically deformed."