water table; groundwater level
Geological term for the upper surface of groundwater. Used in scientific and environmental contexts.
In this area, the water table has been dropping year by year.
Before digging the well, we checked the depth of the groundwater level.
地下水 refers to groundwater itself, while 地下水面 specifically denotes the upper surface or level of that groundwater.
Compound of 地下 (underground) + 水 (water) + 面 (surface/level). The term is a direct conceptual translation of the English 'water table' or 'groundwater level'.