Incidence of Escherichia coli in drinking water: A comparative study of indoor and outdoor sources over four years across Bahia, Brazil

• 8497 samples analyzed, including 7912 outdoor and 585 indoor samples; • 1603 outdoor samples had total coliforms; 501 had thermotolerant coliforms; • Escherichia coli and coliform showed reasonable agreement (k value between 0.21 and 0.4); • The higher incidence of contaminants in the month of august. Waterborne diseases, such as cholera and typhoid fever, pose significant health risks, particularly in areas with inadequate sanitation and contaminated water sources. The Northeast region of Brazil, characterized by limited water resources and high population density, faces challenges in maintaining water quality and distribution. This study aims to evaluate the microbiological quality of drinking water and its relation to the occurrence of waterborne diseases in outdoor environments over a four-year period. A total of 8497 water samples were analyzed, comprising 7912 outdoor and indoor samples and 585 longitudinal indoor samples from a resort-type hotel complex. The study focused on outdoor water sources such as swimming pools, rivers, lakes, and seas. An experimental design was further implemented to assess the microbiological quality of indoor water sources through a longitudinal case study. Among the 7912 outdoor and indoor samples, 1603 showed total coliforms, 501 exhibited growth of thermotolerant coliforms, and 106 tested positive for Escherichia coli (EC). In contrast, indoor samples demonstrated better microbiological quality, with only 18 samples containing total coliforms and none testing positive for EC. Ensuring the microbiological quality of drinking water is vital for public health and the prevention of waterborne diseases. The presence of contaminants in outdoor sources highlights the need for rigorous control mechanisms and monitoring, especially in high-risk regions. Indoor water sources, when properly maintained, can significantly reduce contamination risks, emphasizing the importance of stringent water treatment and hygiene practices.