Demineralised water is specially purified water that has had most or all of its mineral and salt ions removed, such as Calcium, Magnesium, Sodium, Chloride, Sulphate, Nitrate and Bicarbonate. It is also known as Deionised water, DI or Demin water.

Demineralized water is generally defined as having between 1-10 mg/L (ppm) of total dissolved solids (TDS).

The major differences are that demineralised water is usually freer of mineral ions, depending on the number of processes used to make it, and distilled water may have less organic contaminants, as deionisation does not remove uncharged molecules such as viruses or bacteria.

Demineralised water is used for industrial and scientific purposes. Some of the major and common uses are:

• laboratory applications and testing eg.autoclaves
• wash water for computer chip manufacture, and other microelectronics
• automotive uses eg. lead-acid batteries and cooling systems
• high pressure boiler feed
• laser cutting
• steam irons and steam raising applications
• pharmaceutical manufacturing
• cosmetics (‘aqua’ often refers to DI water)
• aquariums
• fire extinguishers

Demineralised water is NOT generally used for drinking water, as it is the minerals in potable water that provide the health benefits and taste. It also tends to remove minerals from food and electrolytes from the body, so it is not usually recommended for drinking or cooking.