This paper suggests a regulatory impact assessment (RIA) to evaluate the potential effects of ‘Resolution law no. 08/2016’ in the Brasília water sector under different perspectives: customers, regulators and local providers. Currently, political/rational and expert/politician terms are not considered integrated parts of the decision process, which could create a non-desirable impact on utility services. Thus, by using the RIA policy tool, regulators would be able to develop a basis for making good decisions rooted in evidence. From that point of view, RIA was set in order to provide the necessary framework capable of considering the multiple dimensions of Resolution law no. 08/2016 (quality of services, safeguarding infrastructural and economic aspects, environmental sustainability and governance) for water services. The multicriteria decision analysis combined with participatory methods were used to support RIA and overcome possible bias from judgments along the process. As a result, the current policy option defined by the regulator did not meet the stakeholders' expectation. Finally, the proposed method can be considered as a useful regulatory tool, which supports effective outcomes with legitimacy.