Guides

• Rain barrel or cistern: why a bigger tank often does nothing — In 2,494 of 3,206 US cities a 55 or 110 gallon barrel is all the storage worth buying for a garden. Where a cistern pays off, and why.
• When rain falls in the wrong season: storing winter rain for a summer garden — In 498 US cities less than 40% of the year's rain falls April to October. 388 of them need a cistern to make rainwater worth it.
• Which states limit how much rainwater you can store? — Colorado and Utah cap household rain storage. In 6 of their 120 cities covered, the cap is below the useful tank size.
• How many gallons does an inch of rain put off your roof? — An inch of rain on 1,000 sq ft of roof is 623 gallons, less what the roof loses. A 55-gallon barrel under a 1,500 sq ft roof is full after 0.07 in.