Mineral water is an excellent drink. There is evidence to suggest that mineral water is beneficial to health, although the body probably doesn't absorb many minerals from it. My only caution is that some mineral waters are high in sodium and should be avoided by people who have high blood pressure.
If you enjoy drinking mineral water, there's no reason to stop. The standard recommendation is to drink at least eight 8-ounce glasses of water or water-based beverages a day, more when you exercise. Try to drink as much as you can and more than you think you need. Always drink more if you are perspiring a lot, which increases water loss.
It is possible to drink too much water. A condition called water intoxication or hyponatremia sometimes affects marathon runners or cyclists who consume large amounts of water over the course of a race. This increases blood plasma (the liquid part of blood) and dilutes the salt content of the blood at the same time that people are losing salt by sweating. The reduced availability of salt to body tissues can interfere with brain, heart, and muscle function.
If you're drinking lots of water because of excessive thirst, see your physician. Excessive thirst can be a sign of diabetes.
Andrew Weil, M.D.