Water with a pH of less than 7 is considered acidic and water with a pH greater than 7 is considered basic. Alkalinity is a measure of the capacity of the water to resist a change in pH that would tend to make the water more acidic. Water with a low enough pH needs to be treated. Any water supply with a pH of less than 6.7 is considered acidic and corrosive. The water will leach metal ions such as: copper, lead, and zinc from the aquifer and attack plumbing fixtures, and piping.
If water has a low pH, you can see the tell-tale, blue-green stains which comes from elevated levels of copper and causes premature damage to piping resulting in pin hole leaks. These blue-green stains are most noticeable on white surfaces that your water comes in contact with such as sinks, tubs and showers, toilets and even white clothing.
Acidic water has also been known to cause discoloration of hair causing blue or green streaks. This reaction to hair is due to the heavy metals leached into your water supply from the corrosive, low pH.