Seepage refers to the slow movement or escape of liquids or gases through small openings or porous materials, like water seeping through a crack in a wall or soil. Full definition
They assume that annually 5 ± 0.5 % of the water impounded seeps into deep aquifers, giving a 1990 rate of seepage of 0.61 to 0.75 mm / yr, and a total volume of 15 mm sea level equivalent. (ipcc.ch)
If you rent a basement unit, you also may request protection against water seepage from the sewers. (pocketsense.com)
We consider that this represents an upper bound, because it is likely that the rate of seepage from any reservoir will decrease with time as the surrounding water table rises, as assumed by Sahagian (2000). (ipcc.ch)