Sustainability reporting is becoming more and more widespread among companies aiming at disclosing their contribution to sustainable development and gaining legitimacy from stakeholders. This is more significant for firms operating in a public services' context and mainly when supplying a fundamental public resource, like water utilities. While the literature on sustainability reporting in the water sector is scant, there is an increasing need to study the usefulness and quality of its sustainability disclosures to adequately inform the stakeholders about the activities of water utilities to protect this fundamental resource and general sustainable development. This article presents a novel assessment framework based on a scoring technique and an empirical analysis on the sustainability reports of Italian water utilities carried out through it. The results highlight a low level of disclosure on the sustainability indicators suggested by the main sustainability reporting guidelines (Global Reporting Initiative, (GRI), and Sustainability Accounting Standard Board, (SASB)); most companies tend to disclose only qualitative information and fail to inform about some material aspects of water management, such as water recycled, network resilience, water sources, and effluent quality. These findings indicate that sustainability reporting is mainly considered as a communication tool, rather than a performance measurement and an accountability tool, but also suggest the need for a new and international industry-specific sustainability reporting standard.