I am often asked if the homeowner should use rain barrels to capture the roof water runoff that would normally go into the rain drain discharge system. Rain barrels can be a positive home groundwater drainage alternative for roof water from the gutters that would normally flow into the rain drain discharges.
While this idea sounds like “green” technology, and may be in some cases, in some cases using rain barrels can lead to more home groundwater problems on the homes foundation. Measures are needed to prevent failure of these systems.
One of the problems with this idea is the fact that a 55 gallon barrel does not hold a lot of water compared to the volume of water that comes off a roof in a day or two of heavy rain. The rain barrel system still needs somewhere to overflow and vent when full. If the barrel overflows and runs against the foundation you will most likely get saturation and hydrostatic pressure at the foundation which causes leaking of groundwater below grade into the basement or crawlspace. If the rain barrels are full, the gutters will overflow causing severe groundwater saturation on the foundation stem wall.
If the homeowner vents this overflow away from the foundation into a larger storage tank buried in the ground, rain barrels may be a feasible and functional idea. The larger buried tank would need proper placement and a pump system with electricity to pump the water out for watering the plants and gardens during the summer. A conceptually solid “green” idea perhaps.
As a practical matter however, the part of your water-sewer bill that is billed for storm sewer and sanitary sewer water discharge is not calculated, it is estimated based on the amount of water that comes out of your faucets for household use. As a result, the reduction in your water bill from not venting that roofwater in the sewers will not be a reality. You will use less tap water to irrigate the gardens however, if the water is stored, and that will reduce your overall water bill.
Rain barrels can be a benefit to the home drainage system, but they must be installed with overflows that prevent the roofwater from overflowing the rain barrels, creating groundwater problems at the foundation area. Make sure you have a solid plan in place prior to jumping into this concept.
Home groundwater drainage knowledge is advised in order to weigh the alternatives and the science behind groundwater removal.