residual amount of water(Amount of water left in a water course after it has fed a hydropower plant in order to maintain a satisfactory dry-weather-flow for allowing the survival of biotic communities)
groundwater(Water that occupies pores and crevices in rock and soil, below the surface and above a layer of impermeable material. It is free to move gravitationally, either downwards towards the impermeable layer or by following a gradient)