Originally when experiments in Japan began to indicate potential health benefits of reduced water, the original explanations went to the notion of alkalinity, because it was the most obvious property of the cathodic outflow. This theory was advanced among others by Dr. Hidemitsu Hayashi, a cardiologist at Kiowa Hospital. Later, research began to focus on the potential antioxidant properties of the water (Prof. Sanetake Sirahata, of Kyushu University), in collaboration with Dr. Hayashi and others (see also Hydrogen Rich Water Saves Mankind by H. Hayashi M.D. & M. Kawamura M.D., October 1999, Tokyo).

Simultaneously, what happens with the mineral load of the water, is as follows: when the filtered water enters the electrolysis chamber, the negative electrodes attract the positive alkaline minerals to their compartment; while the positive electrodes attract the negative acid minerals to theirs. So one side has only alkaline minerals and the other only acid, at which point alkaline water flows out from the Ionizer's top outlet, and acid water from the bottom.

In the past it was thought that the alkaline water contains the minerals essential to our health - calcium, magnesium, sodium, potassium and silicon. It was thought that the health benefits flowed from the fact that this water was therefore highly beneficial in neutralizing body acids. Modern understanding focuses however on the antioxidant potential of the reduced water.

Acid water on the other hand can be used in place of hydrogen peroxide and vinegar, e.g. for washing vegetables. It has a shortage of electrons giving it the ability to oxidize and sterilize.

You can use a simple pH test kit to assess the alkalinity or acidity of the water. Most Water Ionizers include this. You can also test alkaline water's oxidation reduction potential, with an ORP meter.