The Authors describe the main microbiological characteristics of gray and rain waters, the evidence of infections related to the reuse of such waters and the main Italian and international standards and guidelines in this regard. In light of the review, the authors conclude that the limits defined by the Italian regulations are very precautionary and should ensure a very low risk of bacterial and/or viral infection (< 10.5 and 10.9 cases/year). It remains an open problem the risk of parasitic infections, for which the evidences to draw final conclusions are not sufficient yet
