<p>The invention provides a process and an apparatus for effecting that process in which waste water to be cleaned is finely divided into a current of entrainment gas and evaporated. The water vapor formed is superheated, so that the impurities occur as a solid residue and can be collected. The heat of the purified and compressed mixture of entrainment gas and water vapor is used to superheat the water vapor in the current of entrainment gas. An optimal separation between water and the substances contaminating it which cannot be evaporated is accomplished with a low expenditure of energy by introducing the water into a current of inert entrainment gas and by heating the mixture of entrainment gas and water vapor thereby formed, before the separation of the solid particles, in the heat exchange with the purified and compressed mixture of entrainment gas and water vapor by cooling it to below the saturation or dew point temperature.</p>
