Rain gardens are good in all kinds of ways. Catching the runoff reduces storm-sewer overflow, which pollutes waterways with motor oil, pet waste, lawn chemicals, and other contaminants. What's more, rain gardens allow water to percolate into the ground, where it recharges wells and creeks. Mosquitos? No worries, a rain garden drains long before eggs would hatch.
Cost: A typical 10-by-15-foot garden, which would accomodate runoff from about 600 square feet of rooftop, would cost about $600 to $900 to build yourself and about $1,500 to $1,800 if installed by a landscape professional.
Savings: You may be able to earn a discount on your storm-water bill by reducing the area of your property that directs runoff into storm sewers. Check with your water district or public works department (look on your water bill for the customer-service number).
Installation: Do it yourself or hire a landscape professional.
We Like: Rain Gardens: A How-To Manual for Homeowners, which can help you determine whether your site is well-suited to a rain garden and how to design one, step-by-step, if it is. Go to this site for a pdf of the homeowner's manual.