What is double distilled water

Bi-distilled water: what is it?

Multiple distillation

The purity of distilled water is not absolute. It may still contain minimal traces of solute. The measurement of the electrical conductivity provides information about this.

Since the distillation usually takes place in glass flasks, the distilled water obtained can still dissolve small amounts of silica from the glass of the glass flask. Again, this is a minor contamination.

In a second distillation process, vessels made of quartz or platinum are used, which are resistant to the aggressive distilled water.

The resulting distillate after a further distillation is then referred to as double-distilled water.

Alternative names

The chemical and pharmacological nomenclature calls double-distilled water also Aqua double-distillata, or Aqua double-distilled. The term bidestillatus is also used, especially in pharmacology and medicine.

In recipes, Aqua bidestillata is usually referred to as dd. specified.


Double distilled water is used in the manufacture of certain medicines. The usual “aqua purificata”, i.e. ordinary distilled water, is often not sufficient for this due to its lower purity.

Bidestillatus is always bottled sterile in medicine and pharmacology. It can be used as an additive for the production of injection and infusion solutions (e.g. for the production of physical saline solution).

The European Pharmacopoeia always prescribes Bidestillatus for the manufacture of eye drops. It is checked not only with regard to its conductivity, which provides information about the salt content and the ion content. The absence of particles, sterility and the presence of special substances such as heavy metals are also checked.

Alternative manufacturing

As an alternative to production by distillation, production using reverse osmosis and ultrafiltration processes is also permitted in many countries, provided that the water then demonstrably meets the required purity and sterility.

All types of distilled water and osmosis water can have harmful effects on health if consumed over a long period of time. They are not a "cleaning agent" for the human body.