If you've spent more than five minutes in Roblox Studio, you've probably realized that getting a roblox water script to feel just right is a lot harder than it looks. We've all seen the default terrain water—it's fine for some things, but it's heavy, sometimes glitchy, and doesn't always fit the aesthetic of a stylized or low-poly game. If you're trying to build a custom swimming pool, a stylized ocean, or even just a weird purple liquid that acts like water, you're going to have to get your hands dirty with some Luau.
The thing is, "water" in a game engine isn't actually water. It's just a bunch of math and triggers telling the player's character to stop acting like a landlubber and start acting like a fish. When you break it down, a custom script is basically just a way to toggle physics. You're telling the engine, "Hey, the player is inside this box now, so please turn off gravity and let them move vertically."
Why bother with a custom script?
You might be wondering why you shouldn't just use the built-in Terrain Editor. Honestly, terrain water is great for realism, but it's a massive pain to shape. If you want a perfectly square pool on the 50th floor of a skyscraper, trying to paint that water in with the terrain tool is a nightmare. It leaks through walls, it's hard to align, and you can't really "script" how it behaves very easily.
A custom roblox water script gives you total control. You can decide exactly how fast the player swims, how much "fog" they see underwater, and whether they float to the top or sink like a stone. Plus, it's way better for performance if you're making a massive map. A few transparent parts with a script are much lighter on a player's phone or computer than millions of voxels of terrain data.
Setting up the water part
Before you even touch a script, you need the physical object. Usually, this is just a regular Part or a MeshPart. You'll want to make it semi-transparent (maybe a nice light blue) and set CanCollide to false. This is the most important step—if you leave collisions on, your player will just bounce off the surface of the pool like it's made of concrete.
Once you've got your part, you need a way to detect when a player is inside it. In the old days, people used the .Touched event, but let's be real: .Touched is notoriously unreliable. It triggers when a toe hits the water, but it doesn't always tell you when the player leaves. A much better way to handle this in a modern script is using GetPartBoundsInBox or even a simple loop that checks the player's position relative to the water's coordinates.
The logic of swimming physics
When a player enters your water part, you need to change their HumanoidStateType. This is a built-in Roblox feature that handles the animations and movement styles. Usually, you'll want to switch them over to the Swimming state. This automatically triggers those classic swimming animations we're all used to.
But just switching the state isn't enough. If you've ever tried this, you probably noticed that the player just sinks or acts weirdly. You need to handle the buoyancy. You can do this by adding a BodyVelocity or a VectorForce to the player's RootPart. If the player is holding the spacebar, you give them a little upward boost. If they aren't doing anything, you apply just enough force to keep them hovering or slowly sinking. This is where you can get creative—maybe in your game, the water is actually thick maple syrup, so you make the movement much slower and "heavy."
Making it look "wet"
A roblox water script shouldn't just handle physics; it should handle the vibes too. When a player's camera goes below the surface, the whole world should look different. You can do this using a LocalScript that detects the camera's position. If the camera's Y-level is below the water's surface, you can use TweenService to change the Lighting.Atmosphere or add a blue ColorCorrection effect.
It's these little touches that make a game feel polished. Think about it: in most high-quality Roblox games, the transition from air to water isn't just a physical change. There's a sound effect (like a muffled "splash"), a change in the fog color, and maybe some particle effects like bubbles. You can trigger all of this within your main water script by checking the character's velocity when they first hit the part.
Performance and optimization
One mistake I see a lot of new devs make is running a while true do loop on the server for every single piece of water in the game. That is a one-way ticket to Lag City. If you have fifty different pools in your game, you don't want fifty scripts constantly checking for players.
The "pro" way to do it is to handle the detection on the Client. Since the player is the one doing the swimming, their own computer can handle the logic of "Am I in water?" and then just tell the server "Hey, I'm swimming now." This keeps the server's workload light and ensures that the swimming feels responsive. There's nothing worse than a one-second delay between jumping into a lake and the game actually realizing you're supposed to be swimming.
Dealing with different character scales
One thing that often breaks a roblox water script is the variety of character sizes on Roblox. You've got tiny Rthro characters and giant blocky ones. If your script is hardcoded to look for a specific height, it's going to break for half your players.
Always base your checks on the HumanoidRootPart. It's the consistent center of every character, regardless of how many weird accessories or packages they're wearing. If the RootPart is inside the water's boundaries, they're swimming. It sounds simple, but you'd be surprised how many people try to check the distance from the feet, which leads to players "swimming" while standing on the bottom of a shallow pool.
Common mistakes to avoid
One of the funniest (and most annoying) bugs with custom water scripts is the "launcher" glitch. This happens when your buoyancy force is way too high. If a player hits the water at high speed and the script overcompensates by pushing them up, it can launch them into the stratosphere. To fix this, you have to put a "cap" on how much force the script can apply.
Another issue is the "infinite swim." This happens when the script fails to detect that the player has left the water part. They'll just be flying around the map in a swimming animation. Using OverlapParams is a great way to prevent this because you can specifically check for the moment the player is no longer touching that specific water volume.
Wrapping it up
At the end of the day, a good roblox water script is about balance. You want it to be light enough that it doesn't kill the framerate, but detailed enough that it feels like a real environment. Don't be afraid to experiment with the variables. Try changing the gravity, messing with the friction, or adding some custom sounds.
Custom scripts give your game a "feel" that terrain water just can't match. Whether you're building a tropical resort or a flooded basement in a horror game, knowing how to manipulate the player's physics and visuals through a script is a total game-changer. It might take a bit of trial and error to get the buoyancy feeling natural—not too floaty, not too heavy—but once you get it, it makes your game world feel so much more immersive. Just keep testing, keep tweaking, and maybe keep a life vest handy just in case your script decides to launch someone into orbit.