It has been long believed that the graphitic surfaces are hydrophobic. Recent experimental and theoretical works also showed that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite. Here, we show that the water contact angles of freshly prepared supported graphene and graphite surfaces increase when they are exposed to ambient air. By using infrared spectroscopy, X-ray photoelectron spectroscopy and ellipsometry we have demonstrated that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are removed by both thermal annealing and controlled ultraviolet–Ozone treatment. Theoretical calculation also confirms our experimental findings. Our results indicate that graphitic surfaces are intrinsically more hydrophilic than previously believed, and suggest that previously reported data on the water wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air. “In light of the apparently stronger water–graphene interaction, which remains to be explained at the atomic level, most wetting models for graphitic surfaces would need to be revisited. At a more practical level, the performance of graphene-based devices may be more sensitive than expected to environmental humidity and contamination from volatile organic compounds.”