I don’t believe the shader that puddle reflections use is publicly available anywhere, but all shaders that are publicly available are at
...\Steam\steamapps\common\Unturned\Bundles\Sources\Complete_Packages.
If you want to recreate the effect, you’ll have to use a custom shader such as this one.
Sims 4’s Mirrors
I looked online and it seems that running reflections at a high quality kills the frame rate for quite a handful of people, who instead opt to just minimize or disable the setting. The main way they keep frame rate “reasonable” for better hardware is by distorting the reflection as you move away from it. The “whitening” of the mirror that you can see in videos like this “mirror cube” build is just hiding the distortions. They’re the least distorted when you’re closest to the mirror, and that kind of perspective tends to result in the least amount of objects needing to be rendered.
U4 has sideview mirrors on cars. They’re pretty heavily distorted, and angled in such a way that they’re not particularly useful but also don’t render that much. There was originally a rearview mirror, but that one was removed as to help preserve performance overall for more players. Personally, I’d rather it just be a bit distorted and then have a reflection quality setting for mirrors, but 
Two Eyeballs
Two eyeballs doesn’t allow for such trickery, because you have to render all objects twice, even if one eyeball is already rendering it, and then the feature specific to that thread means that the player is actually rendering objects that they can’t see (because if they focus on certain objects they’d technically be able to see past it). Effectively, it’s not possible to aggressively cull objects. More objects have to constantly be rendered, even if the player can’t see it.
Puddle Reflections
When it comes to puddle reflections, they’re usually quite heavily distorted if it’s an actual reflection. Games that are more story-focused and don’t involve you actually entering the water but seem like they have reflections are actually faking it by just copy-pasting the same object, flipping it, and lowering its quality.
Unturned has reflections for its puddles, and at the highest quality quite a handful of people take hefty performance hits. I used to crash on Hawaii if I kept the quality of puddle reflections too high.