Objective: to investigate access and fluoridation of public water supplies in the state of Maranhão. Method: descriptive, direct documentary research, carried out in governmental databases in 2022, also on-site surveys involving 23 municipalities in Maranhão Amazon belonging to the health macro-region IV. The investigated aspects were: population supplied by water; raw water sources; responsible body; water fluoridation and data availability. Only 38% of the population in the macro-region have access to piped water, of which only 44% is treated, the service performed by the state company and those managed by the municipal body were equivalent (48%). 484 sources of collection were identified, 99% underground supplying 92% of the population, this dependence on groundwater reaches 63% throughout the state, surface collection occurs only in the main municipality (5%). Despite the index that 91% of indicator 6.1.1 of the SDGs, the high rural population and the low demographic density constitute a challenge for the expansion of access. No municipality performs artificial fluoridation and there are no records of fluoride levels or previous analyses. There is a direct relationship between a lower HDI and access to potable water. Conclusion: a small part of the population has access to treated water, therefore fluoridation is not guaranteed and the surveillance system needs to be improved.