Artificial intelligence (AI) is increasingly proposed to address deficiencies across water systems, which currently leave about 25% of the global population without clean water, about 50% without sanitation services and about 30% without hygiene facilities. AI is poised to enhance supply insights, catchment management and emergency response, improve treatment plant and distribution network design, operation and maintenance, and advance service availability, demand management and water justice. However, proliferation of this nascent technology could trigger serious and unexpected problems, including system-wide compromise owing to design errors, malfunction and cyberattacks as well as exposures to cascading socio-ecological, water–energy–food nexus and coupled critical infrastructure failures. In response, we make three recommendations for safe and responsible deployment of AI across potable water supply and sewage disposal systems: address gaps in foundational infrastructure and digital literacy; establish institutional, software and hardware mechanisms for trustworthy AI; and prioritize applications based on our proposed systematic benefit and risk assessment framework.