Minecraft – Best way to find all water in certain area in survival Minecraft

An easy way, which you may consider cheating, is using a map viewer.

Without doing that, there are at least two ways:

• Find mossy cobblestone, which is guaranteed to be beside a dungeon (see the first paragraph of the Minecraft Wiki article on dungeons):

• Listen for a mass of zombie or spider sounds underground. They love to make noise and you can hear them through walls, making them easy to find. There's a chance that you'll find an underground cave or a dungeon near them. Creepers do not make noise but there are no such creeper dungeons.

Some guesses:

Levels have relatively little pattern between components like caves and veins so dungeons might be completely randomly placed, even near the top of the levels:

I'd guess that deeper down you have a better chance, but without diving into the code there's no way to confirm this.

Out of interest:

If your goal is to generate a map with lots of dungeons then Minecraft Seeds provides random seeds that do exactly that. Here are three examples:

• Two nearby dungeons after climbing a mountain.
• Three dungeons at spawn if you're too lazy to climb.
• Inside a dungeon if you're too lazy to walk.

Note that an update to map generation could change what a seed produces.

A water block becomes a source block when there's at least 2 other source blocks next to it (not counting diagonally). You start with the very edge and place two water blocks like so. This will give you a 2×2 square of water sources.

__________
|Wo      |
|oW      |
|        |
|        |
|        |

W = water source placed by you
o = water source generated by the water mechanics

Now, simply scoop up any source block (it will refill), and dump it diagonally from the outermost block.

__________
|Woo     |
|oWo     |
|ooW     |
|        |
|        |

Repeat until you hit an edge. Which source block you take doesn't matter, they are all infinite (as in, will refill instantly) at this point.

__________
|Woooo   |
|oWooo   |
|ooWoo   |
|oooWo   |
|ooooW   |

As you can see, to fill an n-long square, you need n bucket loads (actually, only 2, since after that, you can refill from the pool).

To fill the entire rectangle, dump a bucket every other row on one side. The very edge block always has to be filled.

__________
|Wooooooo|
|oWoooooo|
|ooWooooo|
|oooWoooo|
|ooooWWoW|

So to fill an n×m block rectangle, you need n + ceil((m - n) / 2) water sources, with m being the longer side. Again, only 2 if you're talking resources, because after that, you're drawing from an infinite pool.

Here's a video of a guy using this technique on a square:

(Note that he always refills from the still source blocks for some reason, but as noted above, any source block will do.)