The article presents the results of experimental studies on the study of changes in the concentration of active chlorine in water treated with sodium hypochlorite when exposed to UV radiation and its contact with the concrete surface. The obtained research results are aimed at studying and solving the problem of the absence of residual active chlorine in the most remote points of water sampling in large cities with a large length of water distribution networks.

Keywords: disinfection of water, sodium hypochlorite, chlorination, disinfection, residual active chlorine