A dry well or drywell is an underground structure that disposes of unwanted water, most commonly surface runoff and stormwater, in some cases greywater or water used in a groundwater heat pump. 
It is a gravity-fed, vertical underground system that can capture surface water from impervious surfaces, then store and gradually infiltrate the water into the groundwater aquifer. 
Such structures are also called a dead well, absorbing well, negative well and soakaway or soakage pit in the United Kingdom or a soakwell or soak pit in Australia.