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<i>Legionella</i> surveillance is an important issue in public health, linked to the severity of disease and the difficulty associated with eradicating this bacterium from the water environment. Different treatments are suggested to reduce <i>Legionella</i> risk, however long-term studies of their efficiency are lacking. This study focused on the activity of a new formulation of hydrogen peroxide and silver salts, WTP828, in the hospital hot water network (HWN) to contain <i>Legionella</i> contamination during two years of treatment. The effectiveness of WTP828 was tested measuring physical-chemical and microbiological parameters such as <i>Legionella</i>, <i>Pseudomonas aeruginosa</i> (<i>P. aeruginosa</i>), and a heterotopic plate count (HPC) at 36 &#176;C. <i>Legionella</i> isolates were identified by serotyping and genotyping. WTP 828 induced a reduction in <i>Legionella</i>&#8722;positive sites (60% to 36%) and contamination levels (2.12 to 1.7 log₁₀ CFU/L), with isolates belonging to <i>L. pneumophila</i> SG1 (ST1 and ST104), <i>L. anisa</i> and <i>L. rubrilucens</i> widely distributed in HWN. No relevant contamination was found for other parameters tested. The long-term effect of WTP828 on <i>Legionella</i> containment suggest the easy and safe application of this disinfectant, that combined with knowledge of building characteristics, an adequate environmental monitoring and risk assessment plan, become the key elements in preventing <i>Legionella</i> contamination and exposure.