Bound water
Encyclopedia
In hydrology
Hydrology
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...

, bound water, is an extremely thin layer of water surrounding mineral surfaces.

Water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 molecules have a strong electrical
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...

polarity, meaning that there is a very strong positive charge on one end of the molecule and a strong negative charge on the other. This causes the water molecules to bond to each other and to other charged surfaces, such as soil minerals. Clay in particular has a high ability to bond with water molecules.

The strong attraction between these surfaces causes an extremely thin water film (a few molecules thick) to form on the mineral surface. These water molecules are much less mobile than the rest of the water in the soil, and have significant effects on soil dielectric permittivity and freezing-thawing.

In molecular biology and food science, bound water refers to the amount of water in body tissues which are bound to macromolecules or organels. In food science this form of water is practically unavailable for microbiologycal activities so it would not cause quality decreases or pathogene increases.
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