is the water-surface elevation or stage of the free surface of a body of water above or below any datum (see "Gage height"), or the surface of water standing in a well, usually indicative of the position of the water table or other potentiometric surface
{i} water gauge to display level by showing the surface of water in a trough or in a U-shaped tube; height of the water, determination of the quantity of water in a given body of water; water line
The elevation of a particular point or small patch on the surface of a body of water above a specific point or surface, averaged over a period of time sufficiently long to remove the effects of short period disturbances