ISO 21630:2007 prescribes acceptance test methods for submersible mixers used for mixing in wastewater and other applications where at least one system component is a liquid.

"Submersible mixer" is taken to mean a fully submersible aggregate consisting of a drive unit and an axial flow type impeller, and optional parts, such as shrouds, supporting the basic functions.

"Liquid" is taken to mean a body without capacity to accommodate shear stresses when at rest. This includes suspensions and dispersions (liquid/solid, gas/liquid and gas/liquid/solid), and non-Newtonian liquids, provided that a possible small yield stress does not prevent the liquid from flowing when agitated.