For more information on rainwater collecting systems:
www.barefootcollege.org/prog_rwh.htm

If you wanna go Big of a rainwater catching system, check what they do in this school in India. Some of the technologies applied and taught by this school has been used by people for generations and generations. Places where rain does not fall for years, where people don't have access to modern day Stuff . The school is relatively new but the knowledge is relatively old with recently applied modifications.
I saw the barefoot college president speak at a conference and he blew my mind. Simple techs, such as these, can go long way to help
people get access to potable water across the globe
peace