Aqua bidest. stands for aqua bidestillata, which means doubly distilled water in German. Double distilled water is even purer than simple distilled water (aqua dist.). It is produced by a two-stage distillation process in which the water is heated and condensed twice to remove even more impurities.

In scientific and medical laboratories, aqua bidest. is used for applications that require an especially high level of purity. It can be used as a solvent in sensitive chemical reactions, to prepare extra pure solutions and for special cleaning purposes. In histology, Aqua bidest. can be used when a particularly pure water source is required, e.g. in the preparation of certain staining solutions or in procedures requiring high purity.