The aim of this work to estimate the economic benefits that can be generated by the execution of a project to improve the system of wastewater treatment in the city of Puno. Using the contingent valuation method (CVM) with questions referendum and double bounded, it is concluded that the model double bounded has greater theoretical consistency. Average willingness to pay (WTP) of S/4.38 per household is estimated. The people of the south, the main area affected by pollution dumping of wastewater, are more willing to pay than the people of the central and northern part of the city (S/4.90 > S/4.33 > S/3.96). It is confirmed by the payment capacity index (PCI) that the inhabitants of the southern part of the city show greater ability to pay against the inhabitants of the central and north respectively (0.423 > 0.321 > 0.301). Regarding social evaluation of alternative project a net present value (NPV) is estimated of S/8'797,320 with a benefit/cost ratio of S/1.1.