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. The alkaline stream of the treated water is called alkaline water. Proponents claim that consumption of alkaline water results in a variety of health benefits, making it similar to the alternative health practice of alkaline diets. Such claims violate basic principles of chemistry and physiology. There is no medical evidence for any health benefits of alkaline water.
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:
- 2 H2O(l) → 2 H2(g) + O2(g)
- 2 H2O + 2e– → H2 + 2 OH– (at the cathode)
- 2 H2O → 4e− + O2 + 4 H+ (at the anode)
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:
- H+ + OH− → H2O
However, many conventional machines these days use a semi-permeable ion-exchange membrane to separate the two compartments. Therefore, if the concentration of minerals is high enough, the pH of the anolyte can be 4-6 while the pH of the catholyte can be 8-12. Similar machines have been used to produce electrolyzed water which is chemically much different because it also contains sodium hypochlorite, the main ingredient in bleach, and may therefore be used as a disinfectant.
Water ionizers are often marketed on the basis of health claims which are normally focused on their putative ability to make water more alkaline. A wide variety of benefits have been claimed, including the ability to slow aging, prevent disease, offer protection from nuclear fallout, give the body more energy, and offset the effects of acidic foods.
There is no empirical evidence to support these claims, nor the claims that drinking ionized water will have a noticeable effect on the body. Drinking ionized water or alkaline water does not alter the body's pH due to acid-base homeostasis. Additionally, many have inaccurately claimed that the process of electrolysis changes the structure of water from large non-bioavailable water clusters to small bioavailable water clusters, called "micro clusters". However, there is no evidence such changes occur during electrolysis, and these claims not only contradict basic principles of chemistry, , and biology, but if such chemical changes did occur it would be biologically harmful.
- Alkaline diet
- Magnetic water treatment
- Negative air ionization therapy
- Self-ionization of water
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