Well alkaline water basically refers to any water that has a pH that is between 8 and 9. Not only that, the water must also contain alkaline minerals like calcium, silica and potassium.
It's ORP(oxidation reduction potential) must also be low. ORP is basically the ability of water to act as an oxidant or as a reducing agent and as far as alkaline water is concerned this potential should be in the negative.
Alkaline water has long since proven to have some serious health benefits, and although nothing has actually been proven the health benefits include;
1. Supporting the immune system
2. Increased resistance to cancer
3. Shedding weight
4. Detoxification of the body
5. Hydration of the skin and body in general.
Well just like everything on this planet, too much of a good thing is bad so don't go drinking too much alkaline water because as much as it has good side effects on the body, it also has bad side effects on the body. Alkaline water can actually upset the pH of your stomach(increases it) and thus prevents your body from being able to fight off bacteria and other pathogens that are in the stomach.
On the long run, drinking alkaline water will probably do you more good than harm and I think it's a pretty good idea if you want to stay healthy.