Rain barrels allow for the collection of water runoff from roofs and downspouts.  Slowing the flow of water prevents eroding rivulets from forming at a location close to the house. The conserved water reduces the demand for treated water in the household and can be reused in the garden for landscaping watering, or for car washing.

The Alliance for the Cheasapeake Bay has a tremendous, informative link to get you started.  The URL of the Alliance's site regarding rain barrels is http://stormwater.allianceforthebay.org/take-action/structural-bmps/rain-barrels/

Another site, from The Columbia Association on its Watershed management site provides several Quick Tips  on many topics relevant to homeowners.  Below is their Rain Barrel Quick Tip:  

Recycle rainwater. A "rain barrel" is defined as a container that collects and stores rainwater from downspouts and rooftops for future use watering lawns and gardens. A rain barrel may be located on the property provided that it is located on a downspout.  Rain barrels must be made out of a durable material and must be no more than 65 gallons in size.  Rain barrels can be painted and should be maintained in good condition.
Click here to get more Quick Tips.

Live Green, Howard County, has developed a wealth of information and "How To-s" on its website.  Click here to link to that wonderful website.  And be sure to check out the segment of "Additional Links."

There are some rain barrel installation programs within specific areas of Howard County.  Check their website to see if your neighborhood is included in that program.  Commercial sites for rain barrels in a variety of sizes and decorative configurations are also available.