A water ionizer is an appliance that ionizes water. Ionized water is purported to be beneficial to human health and marketed with claims that it is an antioxidant which can slow aging and prevent disease

A water ionizer separates water into alkaline and acid fractions using a process known as electrolysis. It does this by exploiting the electric charge of the calcium and magnesium ions present in nearly all sources of drinking water. When a source of water lacks mineral ions, such as distilled water, or has been filtered by reverse osmosis, electrolysis has no ionizing effect.