Abstract: Process for recovering nitrate from surface and ground water, in particular drinking water, by means of biological denitrification, in which the nitrates contained in the water are reduced to gaseous nitrogen in a reactor by means of a biocatalyst having immobilized cells trapped in a gel or polymer. The "micrococcus denitrificans" that is preferably used requires for its metabolism added hydrogen and carbon that is present in the water in the form of dissolved carbon dioxide. Using a biocatalyst of immobilized cells and of the bacterial strain used, expensive after-purification is unnecessary because of increased bacterial count in the pure water outlet, and no undesirable by-products are formed.