Respiration is an enchantment in Minecraft that can be applied to a helmet and allows you to extend your breathing time underwater. It can be applied to other pieces of armor using commands.
Breathe underwater in Minecraft with the Respiration enchantment
The Respiration enchantment extends your underwater breathing time by +15 seconds per enchantment level in addition to the default 15 seconds. It also gives a chance to not take drowning damage every second per level / (level + 1).
The maximum level that can be obtained without commands is level 3, which gives a total time of 60 seconds underwater before drowning begins. Wearing a turtle shell extends this time by an additional 10 seconds.
Enchantment command for Respiration enchant
Respiration I :
/enchant @p respiration 1
/enchant @p respiration 2
/enchant @p respiration 3