On 21 September 2008, heavy oil penetrated the drinking water supply in Slavonski Brod, Croatia. The accident was caused by the damage of heat exchange units in hot water supply. The system was polluted until the beginning of November, when the pipeline was treated with BIS O 2700 detergent and rinsed with water. Meanwhile, water samples were taken for chemical analysis using spectrometric and titrimetric methods and for microbiological analysis using membrane filtration and total plate count. Mineral oils were determined with infrared spectroscopy. Of the 192 samples taken for mineral oil analysis, 55 were above the maximally allowed concentration (MAC). Five samples were taken for polycyclic aromatic hydrocarbon (PAH), benzene, toluene, ethylbenzene, and xylene analysis (BTEX), but none was above MAC. Epidemiologists conducted a survey about health symptoms among the residents affected by the accident. Thirty-six complained of symptoms such as diarrhoea, stomach cramps, vomiting, rash, eye burning, chills, and gastric disorders.This is the first reported case of drinking water pollution with mineral oil in Slavonski Brod and the accident has raised a number of issues, starting from poor water supply maintenance to glitches in the management of emergencies such as this.