A study by Ahmad and Bajahlan, published in the journal Science Direct, found that  styrene and some other aromatic compounds leach continuously from polystyrene bottles used for packaging.

Quality of plastic and storage time were the major factor in leaching of styrene. Concentration of styrene was increased to 69.53μg/L after one-year storage. In Styrofoam and polystyrene cups studies, hot water was found to be contaminated with styrene and other aromatic compounds. It was observed that temperature played a major role in the leaching of styrene from Styrofoam cups. Paper cups were found to be safe for hot drinks.

The authors concluded that bottled water may not be safer, or healthier, than tap water.