Minecraft wiki entry for Damage, associated text: When the player is no longer submerged in water or is in a bubble column, the air supply regenerates at a rate of 1 bubble every 0.2 seconds (4 game ticks). A Respiration helmet adds an additional on average 15 seconds duration underwater per enchantment level, and a turtle shell adds an additional 10 seconds. Water Breathing and Conduit Power regenerate the air supply. In Bedrock Edition, both effects affect squid and fish.