They save lots of money - and that's just their most obvious benefit.
"Andy Wible’s backyard in Washington, D.C.’s Petworth neighborhood doesn’t look much like a sewerage drain. But his Bayberry, Bee Balm, Iris and Golden Ragwort plants get the job done – and then some. Dug 30 inches* down and filled with a mixture of sand, topsoil and compost, Wible's rain garden draws raindrops tumbling off the roof deep into the soil, purifying them and recharging the groundwater."
Via Karen Russ