Respiration is a helmet enchantment for extending breathing time underwater. It can be applied to other armor pieces using commands.

How do you use respiration in Minecraft?

You can add the Respiration enchantment to any helmet or leather cap using an enchanting table, anvil, or game command. Then you will need to wear the enchanted helmet to gain the extended underwater breathing time. The maximum level for the Respiration enchantment is Level 3.

How long does it take to drown with respiration 3?

With a level 3 respiration enchanted helmet, you get 45 extra seconds of breathing underwater. Furthermore, it's worth noting that respiration also reduces your drowning a bit. So usually when you drown you take 2 damage but with respiration on your helmet you only take 1 damage.