Boron is a mineral that is good for plants in small amounts, but is toxic to some plants in only slightly larger concentrations. Water that contains a lot of calcium and magnesium is said to be hard . Hard water can be softened at a fairly reasonable cost, but it is not always desirable to remove all the minerals that make water hard. Extremely soft water is likely to corrode metals, although it is preferred for laundering, dishwashing, and bathing. Ground water, especially if the water is acidic, in many places contains excessive amounts of iron.
Iron causes reddish stains on plumbing fixtures and clothing.
Like hardness, excessive iron content can be reduced by treatment. A test of the acidity of water is pH, which is a measure of the hydrogen-ion concentration. The pH scale ranges from 0 to 14. For example, water with a pH of 6 has 10 times more hydrogen-ions than water with a pH of 7. According to U.S. Environmental Protection Agency criteria, water for domestic use should have a pH between 5.5 and 9.