Craft a Brewing Stand
Get Blaze Powder to fuel the Brewing Stand
Get Water Bottles
Get Nether Wart
Put Blaze Powder in the Brewing Stand
Place the Water Bottles in the Brewing Stand
Add Nether Wart to make Awkward Potions
Get a Pufferfish
Add the Pufferfish to the Awkward Potions
Collect the Potion of Water Breathing
Optional: Add Redstone Dust to extend the duration to 8 minutes