How do snakes breathe in water?

Snakes cannot breathe underwater because they do not have gills. Snakes are excellent swimmers and can hold their breath for a longer period of time when they are under water.

So the fact is snakes need air to breathe and they cannot breathe underwater. Most of the sea snakes can stay underwater for 30 minutes but they need to come to the surface every 30 minutes to breathe air. Some true sea snakes can stay under water for up to eight hours. 

Snakes are able to absorb 33% oxygen they need through their skin. 

Most of the snakes have 1 lung that stretches throughout their body and some snakes even have 2 lungs.