Surface water is used by 50% of the global population as a source of drinking water. It is therefore important to have an understanding of the quality of surface water used for this purpose, given its potential risk to human health. We studied fecal indicator bacteria [FIB; comprising total coliforms (TC), Escherichia coli (EC) and fecal streptococci] numbers along with 28 other water quality variables in Hoa Binh reservoir, Vietnam during six sampling campaigns undertaken from July 2023 to January 2024. Hoa Binh is a multi-purpose reservoir used for aquaculture, drinking water for local cities and Hanoi, the capital, which is downstream of the reservoir, and irrigation. Of the measured FIB, the mean value of TC exceeded that permitted by the Vietnam technical regulation for surface freshwater, QCVN 08-MT:2023/BTNMT. The mean values of the other variables, except for total nitrogen, were within the limits, although the maximal values of total organic carbon and total phosphorus exceeded them. Different point sources, including those originating from the local human population, tourists, livestock farming and fish cage farming, and diffuse sources from agriculture, comprise the major sources of contamination of the reservoir. Due to the importance of Hoa Binh reservoir for the provision of drinking water for Hanoi, the largest city of Vietnam, our results indicate the need to regularly monitor the quality of the water in the reservoir to provide a scientific basis for the implementation of timely measures to protect it. Our results also contribute to filling the knowledge gap on the microbial quality of water in developing countries.