The best way to soothe the burning sensation in your mouth after eating a hot pepper is to drink milk.
Capsaicin, the compound that makes a pepper hot, is hydrophobic, which means it cannot dissolve in water. Water aggravates the burn by spreading it around your mouth.
Capsaicin can be be picked up by the fats and milk protein, casein. Other fatty foods can work too – peanut butter, cream etc. And, 10% sugar water can give as much relief as milk.