"Rain garden" is a romantic name for a special type of pond, which should feature in every domestic, commercial and industrial garden. Ideally, all the water which falls within a property should flow into the rain garden (technically an 'infiltration pond'). As much of the water as possible should then be infiltrated into the ground within the property boundary. Only the occasional surplus, in times of exceptionally heavy rainfall, should flow into surface water sewers. The reasons for making rain gardens are as follows:
Low Impact Development advice on Rain Gardens
An old London rain garden: all rainwater runoff from the roof is infiltrated into the garden.
Grass swamps are soft, lush are romantic.
Gardens can me at their most beautiful when it is raining