Objectives: In response to the reports of presence of acute watery diarrhea (AWD) in sector I-9/4 of Islamabad, Pakistan, the Federal Disease Surveillance and Response Unit of the National Institute of Health (NIH) Islamabad appointed an outbreak investigation team to confirm the outbreak, identify risk factors and formulate recommendations for control. Methods: A descriptive study was conducted from July 27 to August 20, 2018 to investigate the potential causation of illness and modes of transmission in the outbreak. Active case finding started through a house-to- house case search and the establishment of a case definition. A total of 46 cases of AWD were identified by surveying 508 homes during the study period. Results: The study results revealed that ground bore water (OR 0.1916, CI 0.0633-0.5798, p ＜ 0.0034) and public supply water (OR 6.6182, CI 5.2384-25.3678, p ＜ 0.0027) stored in unsafe utensils for drinking are probable causes of this outbreak. Despite most of these people (n = 30, 65.2%) being aware of the poor quality of the water, they still consuming it. All cases had closed drained toilet facilities at their homes which may have resulted in triggering of the infection. Commonly witnessed signs/symptoms included loss of motion, abdominal cramps, vomiting and fever. People living in this sector belong to an excellentsocio-economic class. Conclusions: The outbreak of AWD in this area revealed that the public water supply may become contaminated at any instance resulting in an outbreak.