The primary purpose of rain gutters is giving water runoff somewhere to go. Gutters help direct the flow of water away from vulnerable parts of your home – including its roof. Indeed, any decent roofing contractor will tell you that no roof is truly complete without a decent set of gutters.
Without gutters, excess water can run off and wreak havoc on various parts of the house
Your existing gutter system is your greatest asset when collecting rainwater. It already conveniently wraps around your entire roof and carries the water runoff away. So, instead of letting all the runoff spill into a drainage area, have it pour directly into your collection tank.
This is the very best way to get as much water as possible into your tank.