What things should be considered when buying a snorkel?

When you first get started with scuba diving, you will have practice time in a swimming pool, followed by practice “dives” in shallow water.  Because of this, most course instructors have their students bring a snorkel.  Even after earning their dive certification, divers typically carry a snorkel when they get ready to descend, helping to conserve air and energy.  A good snorkel should fit your mouth properly, allow water to be purged from the mouthpiece, and have a long barrel with a decent diameter.