Minecraft is a beautiful waste of time. You put so much effort into designing your home, sourcing the materials – if you're playing Survival – and actually laying all the blocks, that it's hard not to be proud of the result. However, when the dust settles and you've almost finished your masterpiece, you start to get a little picky. Building your mansion beside that body of water seemed a good idea at the time, but now it's giving a swamp vibe you're not too sure about.
You can use different methods to remove water in Minecraft, regardless of your situation. It is relatively easy to remove small bodies of water, but bigger ones take time to clear up.
Minecraft: Remove Water Source Blocks
Water in Minecraft emanates from "source blocks." If your water body is simple or small, you might be able to identify them. Make a bucket by placing three iron ingots in a "v" shape in the crafting menu, and then try to identify a source block among the water. If you're dealing with a waterfall, this is easy because the water comes from the top, but in other cases, you need to look at the currents and try to work out where they're coming from.
Use the bucket on a water-containing block you think might be near the source block. If it's the source, the water body dries up because nothing replenishes it. If it isn't, the block you removed refills from the source. Note the direction it fills from and repeat this process until you find the source.
You can also place a block over the source to stop the water from flowing, but if you use the bucket, you can relocate the water or use it for anything you want.
Fill It Up, Burn It Down
If finding the source is unlikely or impossible, you have to remove the water a more difficult way. The two methods for this are essentially ways to streamline the process, and the "fire" method is the quickest. Fill the area of water you want to remove with flammable material, such as leaves, wool or wood. Make sure there are no flammable materials around the edges of the area you want to clear.
When the area is completely full, use a flint and steel to light the flammable material. This removes the material, leaving no traces of the original water.
Using Gravity and Gravel
An alternate method involves using either gravel or sand to speed up the filling and removing part of the process. Get access to the area you want to clear so that you can stand above the surface of the water and fill it with gravel. This isn't difficult because every time you lay a block on the surface, it sinks until that column is full.
Repeat this for every block's worth of water you want to remove. The rest of the job is removing the columns now standing in place of the water. Dig down into one of the corners of the water body, so you have two solid blocks visible underneath the lowest block of gravel. Break the bottom one of these and replace it with a torch.
To clear the gravel or sand, remove the last solid block and allow the others to fall onto the torch. You have to repeat this process for each of the blocks that were occupied by water previously.
Use a Sponge
If you have any sponges (look at Ocean Monuments or defeat an Elder Guardian), you can clear water in Minecraft with a sponge. Build walls to split up the body of water into multiple smaller sections. Place a sponge in the center of each section or on the wall, although the wall placement is less effective at removing water.