guys i noticed a massive plot hole

I'm not sure why I've had to do this over and over and over again on this board. Why are you assuming that H2O is what harms the aliens? Do you truly not realize that the chemical composition of aquifer-drawn water (ground water) is very different than "water" from condensation? Water is not H2O. What we refer to as water in daily human nomenclature covers a very broad range of chemical compositions. The H2O-based solution that condensates or that falls from the sky is quite different than the heavily mineral-enriched composition in the ground, which is what the movie tells us harms the aliens. They clearly run through fog and breathe our air without being harmed. Why do you choose to form a conclusion that directly contradicts what the film shows us?

On the technology factor, that's a different story. If you choose not to like the fact that the aliens somehow got to our planet, hover in the air in lights that hang in the sky, and yet have absolutely no technology to speak of, you're well within reason to do so. The answer to that is that the film is based on modern UFO mythology, which entails some of those same nutty principles like crop circles for navigation, naked aliens running around without technology or with a wand, etc. Pretty much chalking it up to magic and defying the laws of physics.

Another factor is that the intent of the film was to draw upon 50's B-movie tropes, where despite there arriving in a spaceship aliens were almost always monster-like and bestial in nature. Despite those foundations I can see why some wouldn't like the lack of technology or seeming incongruity between beings travelling for thousands of light years but not taking technology with them, although in my view it's quite plausible to chalk it up to cultural bias, societal conditioning, lack of resources after adrift for many generations in space, etc. It's not an actual plot hole, but I can see why some wouldn't like it.

But the water itself is not a plot hole, and is not a legitimate complaint. The movie clearly portrays that ground water (which was drawn via faucet) is what harmed them, and that to be safe they avoided lakes (because ground water feeds into them and to varying degrees they'd possess similar chemical properties, making it alkaline to some extent as opposed to acidic). You're confusing "water" as something that's identical in its composition in all possible forms on Earth, and you're incorrect in that assumption. Regardless of what the specifics might be, the movie clearly shows liquid Earth ground water harming the aliens but no other type of moisture.
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I'm something new entirely. With my own set of rules. I'm Dexter. Boo.