A water ionizer is an appliance

Appliance

Appliance may refer to:* Home appliance, household machines, using electricity or some other energy input** Small appliances** Major appliances...

 that ionize

Ionization

Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...

s water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. Although there is no empirical evidence that ionized water is beneficial to human health, it is marketed with claims that it is an antioxidant

Antioxidant

An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...

 and can slow aging and prevent disease. Such claims contradict basic laws of chemistry and physiology.

Ionization

A water ionizer separates water into alkaline and acid fractions using a process known as electrolysis

Electrolysis

In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

. When a source of water lacks mineral ions, such as distilled water

Distilled water

Distilled water is water that has many of its impurities removed through distillation. Distillation involves boiling the water and then condensing the steam into a clean container.-History:...

, or has been filtered by reverse osmosis

Reverse osmosis

Reverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...

, minerals must be added to water for electrolysis to occur.

Uses

There is no empirical evidence to support claims made by manufacturers that drinking ionized water will have a noticeable effect on the body. Drinking ionized water would not be expected to alter the body's pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

, due to the acid-base homeostasis

Acid-base homeostasis

Acid–base homeostasis is the part of human homeostasis concerning the proper balance between acids and bases, in other words, the pH. The body is very sensitive to its pH level, so strong mechanisms exist to maintain it...

.

Electrolyzed water

Electrolyzed water

Electrolysed water is produced by the electrolysis of ordinary tap water containing dissolved sodium chloride...

 has been used by the food industry to sanitize food products; though effective in bacterial solutions, it was found less useful when sanitizing utensils, surfaces and food products.