Millions of people are resettled each year when dam construction floods their homes and land. Dam building and its associated resettlement may impact water security by altering access to drinking water and sanitation, disrupting aquatic ecosystems, shifting local economies, and undermining the ability to use rivers for income, navigation, and cultural practices. This paper explores how dam-induced-displacement and resettlement in the Brazilian Amazon shaped women’s experiences of water (in)security along four dimensions: Access, Safety, Livelihoods, and Culture. We conducted in-depth interviews with 70 women in the city of Altamira who were impacted by the Belo Monte Dam and who had participated in household surveys before dam construction began. Our findings suggest that dam building and resettlement did not universally improve or degrade water security, but rather shifted it in uneven ways. While access to water improved for some women, the majority of respondents experienced water outages after the dam, some for weeks at a time. Safety from seasonal flooding and access to sanitation improved for many, though poor water quality and lack of maintenance of sanitation infrastructure created problems. Finally, resettlement and changes in river ecology undermined livelihoods for fisheries-dependent households and severed cultural connections to the river for many. These findings have crucial implications for health outcomes and can inform policies to improve the water security and well-being of populations resettled due to future dams, other development projects, and climate change.