Objective: The purpose of this research was to verify the determinants of the voluntary web-based disclosure of the Brazilian Bavarian sewerage companies.Basis: This is a study based on the theory of the Agency, the theory of referral, the theory of legality and the theory of political costs. Method: A metric has been developed to assess the extent of voluntary web-based disclosure. The sample consisted of 68 companies registered in the National Sanitation Information System (SNIS) providing water services, sewage services or both, incorporated under the annous company regime. The factors examined were Tamanho, Type of Audit, Third Party Capital Cost, Property Structure, Regulation, Rentability, Leverage and Liquidity. Multiple regression was used using a generalised linear model.Results: An association between audit type and ownership structure with a higher level of voluntary web-based disclosure was verified. However, the variables Tamanho, Regulation, Cost of Capital, Rentability, Leverage and Liquidity were not statistically significant. Contributions: The findings of this research contribute to a better understanding of the factors explaining the degree of voluntary web-based disclosure of Brazilian sewerage companies which, when providing public services, have a commitment to act more transparently. In addition, there is insight into the role of the ownership structure in the disclosure level of the companies.