How to Build Underwater in Minecraft

Building underwater in Minecraft is one of the most impressive things you can do, but it comes with unique challenges. You move slowly, you drown, blocks behave differently when waterlogged, and clearing water from enclosed spaces is tedious without the right tools. This guide covers everything you need to build a functional and good-looking underwater base.

Breathing underwater

Before you can build, you need to not die. There are several ways to breathe underwater:

• Potion of Water Breathing, brewed from a Pufferfish added to an Awkward Potion. The extended version lasts 8 minutes. This is the most accessible method early on.
• Respiration III helmet enchantment, extends underwater breathing time to 60 seconds (from the default 15) and slows suffocation damage. Combine with Water Breathing potions for maximum uptime.
• Turtle Shell helmet, crafted from 5 scutes (baby turtles drop scutes when they grow up). Gives 10 seconds of Water Breathing when you enter water. Stack with Respiration III for 70 seconds total.
• Conduit, the ultimate solution. When activated, it grants permanent Water Breathing, Night Vision and Haste to all players within range. More on this below.

Setting up a conduit

A conduit is the underwater equivalent of a beacon. To craft it, you need 1 Heart of the Sea (found only in buried treasure chests, use a treasure map from underwater ruins or shipwrecks) and 8 Nautilus Shells (from fishing, drowned mobs, or wandering traders).

To activate the conduit:

• Build a frame from Prismarine, Prismarine Bricks, Dark Prismarine, or Sea Lanterns. These are found in Ocean Monuments.
• The minimum activation requires 16 blocks arranged in a 5x5 open frame (a square ring) around the conduit. This gives a range of 32 blocks.
• A full frame uses 42 blocks arranged in three 5x5 rings on all three axes (X, Y, Z) around the conduit. This maximizes the range to 96 blocks and also activates the conduit's attack ability, which damages hostile mobs nearby.
• The conduit must be in water, and the frame must be in water. Place the conduit in the center of the frame structure.

With a fully powered conduit, you can build comfortably in a large underwater area without worrying about air.

Draining water with sponges

Sponges are the fastest way to remove water from an enclosed space. Each sponge absorbs up to 65 water blocks in a 7x7x7 area. After absorbing, it becomes a Wet Sponge, which you dry in a furnace (put a bucket in the fuel output slot to collect the water).

Where to get sponges:

• Ocean Monuments, sponge rooms contain 30 wet sponges each. Not every monument has a sponge room, but most do. You also get sponges from killing Elder Guardians.
• Sponges are reusable after drying, so a single monument raid gives you enough for most builds.

To drain a room:

• Build the walls and ceiling of your room first, fully enclosing the space. Use any non-waterlogged solid block.
• Place sponges starting from the top corners. Water flows downward, so clearing from the top prevents re-flooding.
• Work in sections if the room is large. Build internal temporary walls to divide the space, drain each section, then remove the dividers.
• Collect wet sponges, smelt them, and reuse.

Alternative draining without sponges

If you do not have sponges yet, you can use these slower methods:

• Sand/gravel gravity blocks, fill the enclosed space with sand from the top. Sand falls and displaces all water. Then mine out the sand.
• Fence/sign method, signs and fences block water flow without being full blocks. Use them to segment the space and clear water section by section with empty buckets.
• Kelp trick, if water blocks are not source blocks (they are flowing), plant kelp to convert them to sources, then break the kelp and sponge up the sources. Or use this in reverse to prevent flow.

Waterlogged blocks: what to know

Many non-full blocks can be waterlogged, meaning water exists inside them. Slabs, stairs, fences, chests, signs, trapdoors, chains, and lanterns are all waterlogged when placed in water. This means:

• Placing a bottom slab in water does not remove the water, the slab becomes waterlogged and water flows through it.
• To keep water out, use full solid blocks for walls and floors. Glass, concrete, stone and wool all work.
• If you want decorative slabs or stairs inside your base, place them after draining the room.

Building tips for underwater bases

• Use glass for walls and ceilings. An underwater base with opaque walls is just a buried base. Glass lets you see the ocean, which is the entire point.
• Sea lanterns and glowstone are good light sources that fit the underwater theme. Froglights also work well.
• Build tunnels between rooms using glass panes for a corridor effect. 3-wide tunnels with glass pane walls look great.
• Depth Strider III boots let you walk at normal speed underwater during construction. Aqua Affinity on your helmet lets you mine at normal speed.
• Use doors or signs for emergency air pockets during construction before the conduit is active. Doors placed underwater create a 1-block air space.
• Consider building at a moderate depth (Y 40-50) rather than the ocean floor. You get the underwater vibe without the extreme darkness and pressure of the deep ocean.

If you want to skip the setup hassle, join Astroworld MC, IP play.astroworldmc.com. Java + Bedrock, no install required.

Underwater builds require more preparation than surface builds, but the visual payoff is massive. Get a conduit working first, raid a monument for sponges, bring Depth Strider boots and lots of glass, and you will have a base that looks unlike anything else in the game.