Unlike acidic water which has a pH below 7 (neutral), alkaline water is mineral-rich and has a pH above 7. Proponents of drinking alkaline water believe that alkaline water has many health benefits that include hydrating and neutralizing acidic blood, which results in other benefits such as detoxifying the body, energizing, acting as an antioxidant, protecting bones, and aiding in elimination.
However, clinical research has not been able to validate these benefits. According to Gabe Mirkin, MD, dietary modification cannot change the acidity of any part of your body except your urine. The pH balance is under very tight physiological control and the body pH remains in balance regardless of what you eat or drink. If the blood pH drops from consuming too much protein, the body quickly balances the pH with calcium from bones. And as far as hydration, all water is hydrating.
The bottom line, according to Andrew Weil, MD, is that the health claims for water ionizers and alkaline water are bogus.