drainage
n. uncountablen. the system or process that carries away extra water or waste liquid from an area. Good drainage keeps your garden from turning into a swamp after it rains.
n. the natural or artificial removal of surface and sub-surface water from a given area. Often refers to the infrastructure of pipes and channels designed to prevent flooding or waterlogging.
The field has poor drainage and stays wet for days.
Engineers are improving the city's drainage to handle the heavy rainfall expected during the hurricane season.
The architect emphasized that without a sophisticated drainage system, the coastal development would be vulnerable to soil erosion and structural instability within a decade.
From drain + -age.
Uncountable when referring to the process or system in general; rarely used in the plural.