This paper studies the economic efficiency of the treatment plants of Empresa de Acueducto y Alcantarillado de Bogotá.To do this, we will estimate the cost of the two treatment plants systems, North (Wiesner and Tibitoc plants) and South (Vitelma, Dorado and Yomasa plants).By adjusting regression models with ARIMA errors, and analyzing the elasticities obtained for each cost in each system, we found that the southern system is more efficient in the use of inputs, while the northern system has a more efficient administrative structure.Therefore, and considering the relative weights of each factor, we find that the southern system is more efficient than the northern system.