This article reports the findings of a two-year transdisciplinary research project that explored the implications of climate change for the security and safety of drinking water supplies in three communities in Te Hiku o te Ika in Aotearoa New Zealand. In this region, potable water comes mainly from “roof and tank” systems. The project was designed as integrative Kaupapa Māori research utilising climate science, microbiology and social science to develop community-oriented approaches for dealing with the complex issues at the nexus of climate change. Evidence-based advice and practical suggestions tailored to specific locations were developed by drawing on climate change projections, local mātauranga Māori and drinking water studies. Interviews with kaumātua surfaced long-standing knowledge and experience of the climate and its variations in Te Hiku. Computer-based scenario modelling—using both automated and community-collected data on precipitation and temperature—produced 80-year climate change projections of water security. Health-focused Escherichia coli studies revealed the current water quality and used climate data to predict future water quality. Overall, this research reinforces arguments in the literature that the findings of transdisciplinary studies can provide more explanatory power than single-discipline research.