Water ionizer

A water ionizer (also known as an alkaline ionizer) is a home appliance which claims to raise the pH of drinking water by using electrolysis to separate the incoming water stream into acidic and alkaline components. Proponents claim that consumption of the alkaline stream results in a variety of health benefits, making it similar to the alternative health practice of alkaline diets. Such claims are not accepted in chemistry, physiology, and evidence-based medicine.

The machines originally became popular in Japan and other far eastern countries before becoming available in the U.S. and Europe.

Despite being described as 'water ionizers' the machines are designed to work as water electrolyzers. This is an electrochemical process in which water is split to form hydrogen and oxygen by an electric current. The overall chemical reaction is shown below:

During this process, the water near the anode is acidic while the water near the cathode is alkaline.

Water ionizers work by simply siphoning off the water near the cathode. Water siphoned off the cathode side contains increased levels of hydroxide (OH⁻) and would be expected to have a higher pH (i.e. be more alkaline), whereas water siphoned off near the anode would have increased levels of H⁺ making it acidic. The acidic water is claimed to be useful for household disinfecting.

The effectiveness of the process is debatable because electrolysis requires significant amounts of time and power; hence, the amount of hydroxide that could be generated in a fast moving stream of water such as a running tap would be minimal at best. Additionally, the process of reversing the reaction requires much less energy, so if the area between the alkaline and acidic water is at least semi-permeable, the water will undergo another reaction that just leaves neutral water. The second reaction is shown below:

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