This study focuses on the companies of the Águas de Portugal Group, which operate in the water and sanitation sector, and aims to perform a content analysis of the auditor's reports and, specifically, of the key audit matters (KAM) disclosed from 2017 to 2021. Although it is not mandatory to disclose KAM, 57% of companies disclosed KAM in the period under review. Content analysis shows a high similarity in the number and content of KAM disclosed by companies in the period in which the same firm audits them. The categories of KAM disclosed are investment - recognition and measurement; impairment of investments; impairment of debts; revenue - recognition of downward activity; revenue - expense recovery deviations; and process of split. Audit responses to disclosed KAM mainly included inspections, followed by analytical procedures and inquiries, with reperformance being the least common procedure.