Pure water is pH neutral, measuring 7.0 on the 1-to-14 pH scale. Anything above that is alkaline (and anything below is acidic).
Pure water passes through the digestive tract with minimal absorption, but the minerals in alkalized water purportedly increase absorption that hydrates cells throughout the body. Some alternative medicine practitioners believe this hydrating effect can cure or prevent many diseases.
Pro: Fights Free Radicals
The electrolysis process that ionizes minerals causes alkalinity. The negatively charged molecules in alkaline water then may capture and neutralize positively charged free radicals in the body that damage DNA and cause cells to age drastically.
Pro: Treats Diseases
Patients suffering from a variety of conditions—including diabetes, liver diseases, gastroduodenal ulcers, asthma, allergic disorders, high or low blood pressure and osteoporosis—report perceived improvement from drinking alkaline water. Because cancer cells cannot grow in an alkaline environment, some believe alkaline water may treat or prevent cancer.
Con: Does Not Balance pH
Most of what we drink and eat, from orange juice and coffee to tomatoes and beef, is acidic. Some believe drinking alkaline water may counter the acidity of these foods and restore a more balanced pH in the body. But alkaline water likely has no effect on pH, which varies widely throughout the body. The human body expels excess acid in its own tried-and-true ways, including through sweat, urine and just plain breathing.
Con: Does Not Change the pH of the Stomach
Hydrochloric acid in the stomach has a pH of about 2, which is corrosive enough to eat through metal and certainly strong enough to counteract the negative ions in alkaline water. Everything that passes through the stomach becomes highly acidic, so alkaline water doesn't really stand a chance.
Con: Does Not Change the pH of the Intestines
After acidification in the stomach, strongly alkaline enzymes in the intestines further break down food to advance digestion. The slight alkalinity of alkaline water would not affect the pH of the intestines even if it retained that alkalinity when passing through the stomach.
Con: It's Expensive
Bottled alkaline water at the market is definitely a luxury. Even at home, a system can get pretty pricey: Ionizers that convert pure water into alkaline water range from $100 to over $4,000, and they also require maintenance and filter replacements.
Pure H2O is probably the way to go.