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Hard water

Water that contains a great number of positive ions. The hardness is determined by the number of calcium and magnesium atoms present. Soap usually dissolves badly in hard water.


A water-quality indication of the concentration of alkaline salts in water, mainly calcium and magnesium. If the water you use is "hard" then more soap, detergent or shampoo is necessary to raise a lather.

Hydraulic conductivity

The rate at which water can move through a permeable medium.


The science of chemistry and movement of groundwater.


A chart that measures the amount of water flowing past a point as a function of time.

Hydrologic cycle

The natural cycle of water passing through the environment, including evaporation, condensation, retention and run-off.


Branch of science concerned with the properties of the Earth's water, and especially its movement in relation to land.


Having an affinity for water.


Having an aversion for water.

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