Minecraft: Edition

1) Load up a tutorial world, once loaded in press "b" to skip tutorial.

2) Run straight through the tunnel, down the staircase and take your first right.

3) Now we are at the brewing station; coordinates (X:5, Y:79, Z:41), open the chest behind the brewing stand and collect the "(10) glass bottles", "(10) Nether Wart", and "(10) Blaze Powder".

4) Turn to your right and use "left trigger" to fill "(3) Glass Bottles" with water turning them into "Water Bottles".

5) Turn around and run to the entrance of the brewing stand area, turn right and walk up a small set of stairs, turn left and then down a small set of stairs, keep walking straight through the villager area and take a right when entering the farming area just after the villagers.

6) Now we are at the fishing station; coordinates (X:-57, Y:78:, Z:-70). Open the chest and collect the fishing rod.

7) Turn right and walk to the end of the dock facing the water, use "left trigger" to start fishing. When a fish has been caught, your lure will dip up and down, once this is happening use "left trigger" to catch the fish. Do this until you catch a "Puffer Fish".

Now that we have a caught our "Puffer Fish" we have all the necessary ingrediants to brew the "Potion of Water Breathing 3:00".

8) Run back to the brewing station; coordinates (X:5, Y:79:, Z:41) and place "(10) Blaze Powder" into the upper left corner for fuel, "(2) Water Bottles" in the bottom left, "(1) Glass Bottle in the bottom right, and then "Nether Wart" in middle top, once the "Nether Wart" has brewed, then place the "Puffer Fish" in the middle top.

You have now succefully brewed a "Potion of Water Breathing 3:00", go jump in some water above your head, drink the potion using "left trigger" and wait (2) minutes for the achievement to pop!

Start up a mini-game and make sure it isn't an online game.

From here you're placed in the waiting area for mini-games and can roam around the pre-built map and cannot take any form of damage.

Head over to the fountain or pond near the center and submerge yourself. After 2 minutes you should have the achievement without the need of potions.

Here is a quick guide on how to make underwater breathing potion in the tutorial world.

This achievement is pretty simple. You'll need to create a potion of water breathing which requires a water bottle, 1 nether wart and 1 pufferfish. Consume the potion and submerge yourself underwater for 2 minutes. The effect will last 3 minutes so you'll only need one.

EDIT: For those of you like myself that aren't too fond of fishing in Minecraft and may not know, pufferfish are obtained by fishing.

EDIT: Another tip since they've changed it in one of the latest updates - You're going to need blaze powder on a brewing stand to "power" it like you would coal in a furnace. So make sure you collect a good amount of blaze rods in the nether. That way you'll have no problem brewing potions later on.

You'll need a brewing stand to start, then a nether wart, a puffer fish, blaze powderx2 and a water bottle. Once that's done mix the wart first then the pufferfish with the same water bottle to get the underwater potion. Then find the nearest water and jump in and drink up, then wait 2 minutes for the achievement.
If doing this in tutorial mode all items required except a puffer fish can be found at X:7 Y:79 Z:-41in a chest. You can find the puffer fish in the fishing tutorial area, use the rod in the chest there to catch it. Thank you "Virgin" for that information.

So here’s what I did and it worked like a charm, host a public battle game run to the area with water and jump in. Stay there for 2 minutes and the achievement is yours, easy as that

If anyone joins just boot them

short video!