water level

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The level of the surface of a body of water.
• noun The water line of a ship.

from The Century Dictionary.

• noun In mining, a heading or gangway so nearly horizontal that drainage water in it flows very sluggishly or hardly at all.
• noun The surface of the water in any vessel or reservoir, natural or artificial, in which water is standing, as in a well, canal, pond, lake, etc.; also, the plane of saturation beneath the surface of the ground, or the plane below which the soil or rock remains saturated with water under the ordinary conditions of rainfall, etc.
• noun A leveling-instvument in which water is emploved instead of mercurv or spirit of wine.

from the GNU version of the Collaborative International Dictionary of English.

• The level formed by the surface of still water.
• A kind of leveling instrument. See under Level, n.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The level of a body of water, especially when measured above a datum line
• noun The level of the water table below ground
• noun The waterline of a ship

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun underground surface below which the ground is wholly saturated with water
• noun a line corresponding to the surface of the water when the vessel is afloat on an even keel; often painted on the hull of a ship
• noun a water gauge that shows the level by showing the surface of the water in a trough or U-shaped tube
• noun the level of the surface of a body of water