What is the potential hydrogen of water?
Alkaline is a water which has a potential hydrogen (ph) higher than 8.0.  Water with a PH of 7.0 is distilled water, and water with a ph less than 7.0 is considered to be acidic.  Alkaline water is supposed to be better for the body but you can argue that the acid in the stomach neutralizes the alkalinity so it doesn't have any health effect on the body.  More research is needed to say whether or not alkaline water with a high PH is actually good for you.