Renew is a non-chlorine shock treatment. This fast-dissolving granular rids spa water of residual soaps, deodorants, natural oils and organic materials that can build up in spa water. When Renew is added to the spa water, it reacts with the bromide and forms a bromine solution to destroy any microorganisms left behind by the bather. Part of the Reserve & Renew® Chlorine-Free Sanitizing System.