We analyze by means of frontier methods (input requirement function) the relative energy efficiency of urban water and sanitation providers in Brazil. We estimate energy savings through measures the sector could implement on variables which control. We find a 63 percent efficiency average, with respect to best practices in the sample (the frontier). We estimate that a 10 percent reduction in unaccounted-for water can reduce 4.2 percent the electricity consumption for the whole sample; also, a reduction in 10 percent of the breach of coverage between sanitation and water can achieve reductions of 1.45 percent in the input under study