Question: **Aliens, for some unknown reason, want all the water (H2O) in our oceans, seas, lakes, rivers, (all large bodies of water on earth), and plan to steal it from us overnight.** 

Luckily for us, they don't want to wreck life on this planet. 

As highly advanced lifeforms, they have the technology to replace all our water with an equivalent amount of "magic liquid". We don't know why they can't make H2O - they just can't, but they can make anything else.

**So the question is: Is there a replacement for H2O that the aliens can replace our water with that won't destroy life as we know it? This chemical compound should have most (if not all) of the properties of H2O.** 

**Note:** How they manage to do this is irrelevant. You can assume that by some hand-waved process, all the H2O just gets replaced with the aforementioned magic liquid instantaneously.

Answer: 
I believe the answer is "NO". Water is water is water. On top of that, hydrogen and oxygen are two of the most abundant elements in the universe. Stealing it from a populated planet (where you don't want to hurt the lifeforms) is madness.
[Dihydrogen Monoxide](http://www.dhmo.org/facts.html)
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![enter image description here](https://i.stack.imgur.com/znhbN.gif)

Dihydrogen Monoxide is a clear liquid, mostly flavourless chemical that is often used in pesticide production and distribution which can effectively replace water in an ecosystem. When sprayed over crops it was discovered that DHMO had an almost *identical* affect on the crops growth as naturally occurring water. Shortly after pure DHMO is introduced into an ecosystem it quickly absorbs minerals in solution making it almost indistinguishable from real water that falls as precipitation! 

There are a few ways to detect dihydrogen monoxide however: it is highly reactive with pure sodium, lithium and potassium (as in explosive reactive), and when poured over iron, it can cause a redox reaction that will turn the iron red and make it brittle. 

But you can drink it, you can swim in it, and you can even make ice with it! To the naked eye, and without specialized equipment, it would be *impossible* for the average person to distinguish DHMO from H2O.

You can learn more about **DHMO** here: [Frequently Asked Questions About Dihydrogen Monoxide (DHMO) What is Dihydrogen Monoxide?](http://www.dhmo.org/facts.html)