"By capturing rainwater, some homeowners are breaking the law. This has put
city and state governments in an awkward position-smack in the middle of
competing water users and advocates, often from within their own agencies,
of conserving water to protect supplies."

http://www.popularmechanics.com/scie...h/4314447.html

Some say rainwater should follow its natural course instead of being
diverted by homeowners so that the homeowner's betters can allocate the
water based on need - or political pressure - to those more, um, worthy of
wetting.

It's for the children.