It was found by the fluorimetric method using 2,3-diaminonaphthalene that moderate heating of water (60-80°C, for up to 4 h) leads to the fixation of atmospheric nitrogen with the formation of nitrite. The kinetic parameters of this process were determined. The energy of activation of [Formula: see text]formation was estimated to be 139 kJ/mol. It was found that the amount of nitrite formed depends on the concentration of dissolved oxygen and nitrogen. It was shown by two independent methods (Griess reagent/VCl3 and 2,3-diaminonaphthalene/nitrate reductase) that heating of water (80°C, 1 h) results in the formation of nitrate; with the use of the fluorescent probe dihydrorhodamine 123, the generation of nitrogen dioxide (peroxynitrite) was revealed. Nitrite, nitrate, and nitrogen dioxide are formed in water upon heating in approximately equal amounts. A scheme of reactions proceeding with bidistilled water by the action of heat with the formation of nitrogen oxides is proposed.