In 2015 the city of Arequipa - Peru, with more than a million inhabitants, had a single wastewater treatment plant, that could only serve 8% of the wastewater produced by its population, the rest was dumped into a natural water body without any treatment, affecting its environmental quality. To solve this problem, and stop polluting, two wastewater treatment plants have been built, La Escalerilla and La Enlozada, with the capacity to meet the total demand for wastewater treatment. This article has evaluated the progress in Target 3 of Sustainable Development Goal 6 by the Improvement of Wastewater Treatment in Arequipa-Peru, which seeks to guarantee the availability of clean water and sanitation for all. Target 3 refers to treating wastewater safely. To determine the indicators for this Target, the methodology proposed by the United Nations has been used, which is applied worldwide by the states that signed the 2030 Agenda agreement, and its application has been tested with real data. In this study, the effectiveness of the measure has been evaluated and it has been concluded that the target 6.3 has been achieved. To determine the value of the indicators, baseline information (Before treatment) and five years monitoring (2016-2020) have been compiled, the period in which the Wastewater Treatment Plants have been operating. The conclusions serve to assess the closure of gaps and verify the sustainability of what has been implemented that is aligned with policy number 33, "Water Resources Management" of the Peruvian Government.