A quality of water measured by the pH scale. This scale goes from 0 to 14. 0 is the most acidic and 14 is the most alkaline (opposite of acidic). Something with a pH value of 7 is neutral, this means that it is neither acidic nor alkaline. Acidity is measured to determine water quality. In the mining industry, for instance, it is important to know the acidity of a solution since this can create highly acidic waters through run-off waste–a serious environmental problem.