Bi-distilled water: what is it?

Again and again you hear of bi-distilled water. What this is exactly, why and where it is used, and what distinguishes it from ordinary distilled water is explained here.

Multiple distillations

The purity of distilled water is not absolute. It may still contain minimal traces of solutes. An explanation of this is the measurement of the electrical conductivity.

Since the distillation usually takes place in glass flasks, the recovered distilled water can still liberate small amounts of silica from the glass of the glass flask. This again represents a minor contamination.

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

The resulting distillate after further distillation is then referred to as bidistilled water.

Alternative names

The chemical and pharmacological nomenclature calls bidistilled water also aqua bidestillata, or aqua bidest. Especially in pharmacology and medicine, the term Bidestillatus is common.

In recipes, Aqua bidestillata is usually called dd. specified.


Double distilled water is used for the manufacture of certain medicines. The usual "Aqua purificata", ie ordinary distilled water is often not sufficient because of its lower purity.

Bidestillatus is always filled sterile in medicine and pharmacology. It can be used as an additive for the preparation of injection and infusion solutions (for example for the preparation of physical saline solution).

The European Pharmacopoeia also always prescribes Bidestillatus for the preparation of eye drops. Its verification is not only in terms of its conductivity, which gives information about the salt content and the ion content. Particle freedom, sterility and the occurrence of special substances, such as heavy metals, are additionally tested.

Alternative production

As an alternative to production by distillation, production in many countries is also permitted by means of reverse osmosis and ultrafiltration processes if the water subsequently proves to fulfill the required purity and sterility.

Tips & Tricks

All types of distilled water and osmosis water can have a harmful effect on long-term enjoyment. They are not a "cleanser" for the human body.

Video Board: Double Distilled Water Test