Water mites have three active stages, the six-legged larva, the eight-legged deutonymph, and the eight-legged adult. There are also two inactive pupa-like stages: the protonymph (between larva and deutonymph) and the tritonymph (between deutonymph and adult).

Deutonymphs are often collected along with adult mites, as they share the same habitats and diets. They have no genital opening and have a reduced number of genital acetabula relative to conspecific adults. They also tend to be more poorly sclerotised than adults. In sexually dimorphic species, the deutonymph resembles the female more than it does the male.

Deutonymphs of some taxa (e.g. Hydrodromidae, Hydrachnidae) look very much like adults and may be identified using this key; however, most will not be identifiable. It is sometimes possible to associate deutonymphs with co-occurring adults based on palp and leg morphology.

There are no published keys to the larval or deutonymphal stages of water mites from Australia.