Why do mints make your mouth feel cold?
The feeling of cold from mints is caused by menthol. Menthol affects the TRPM8 receptor on skin and also in the mouth. TRPM8 is also a general cold receptor: so if you are in contact with menthol the receptor reacts just like when you are exposed to cold (Bautista et al., 2007).

The receptor is strongly activated at temperatures below 26 degrees Celsius (Bautista et al., 2007). Drinking water is usually colder than that. So if you ate mints and drink cold water afterwards, the receptor response is even stronger.