Water level

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Weir on the Isar near Hinterbrühler See
Underground water level in the St. Beatus Caves

In geosciences and technology, the water level is the smoothed shape of a free, largely undisturbed water surface , as it appears under the influence of gravity .

A water level smoothed in this way represents an equipotential surface in which communicating vessels have exactly the same value of gravity potential . A distinction must be made between the terms “water level” (see below) and water level . The theory of equipotential surfaces applies in all types of liquid containers or in pipelines when they are not under pressure and have no noticeable adhesion or friction .


When forces other than air pressure act, currents and waves occur. By averaging repeated measurements over a certain period of time, it is possible to determine the undisturbed surface that is normal to the plumb lines everywhere . For more demanding tasks, a so-called reduction of the measurement data is carried out instead of averaging , whereby the disruptive forces must be modeled mathematically .

The considered water surface can be the surface of seas (see geoid ) or of inland water ( rivers , larger streams , cave water ).

Difference between water level and water level

In contrast, the term " water level " means something else:

Idealized, smooth surface

While on a small scale - for example in laboratory technology  - only minor influences disturb the water level (for example the edge and surface tension ), this is different in nature. There the water level is defined as the dynamic mean value of an idealized, smooth surface and, above all, abstracted from the following influences:

Mirror type

Before polished metals and glasses were made usable, water levels were used as mirrors , which is thematized in the ancient Narcissus saga : Narcissus sees himself in the water level for the first time. In the 19th century, fictional water levels served to justify the direction of illumination of the limelight in the theater. To this day, the reflections from water levels are used in landscape architecture or light art and are a challenge for artistic images.

Science and psychology

Deviations from the normal of the horizontal smooth surface play a role in numerous experiments and scientific demonstrations. Isaac Newton used a water mirror in his bucket experiment to show the gravitational forces in a rotating vessel. Jean Piaget put test subjects to the test in connection with his “Theory of Mental Development” by having them draw the water level in an inclined glass.

Web links

Wiktionary: water level  - explanations of meanings, word origins, synonyms, translations