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: 
Since the question specifically wants to use water from Earth (damn, these aliens are insistent), I returned to the drawing board to rethink my approach. My first reaction to this question was to refute it, but I decided to take a look at what substitutes for water were already known and, to my extreme surprise, there is one that is pretty close.

[Formamide](http://en.wikipedia.org/wiki/Formamide) has demonstrated viability as an alternative solvent to water. It can dissolve most things that dissolve in water. This chemical was originally brought to my attention by [this paper](http://pubs.acs.org/doi/pdf/10.1021/j100280a081), for those who have access to *The Journal of Physical Chemistry*.

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I am leaving this part of the answer here for posterity reasons.

Since these aliens are in dire need of water and (for whatever reason) can only use H2O despite its similarity to an easily fabricated liquid, we, as Earthlings intent on preserving our precious little pearl of a planet, should erect a giant sign in space that says:

$$\large \text{Go to Europa for Water}$$

There are [several places](http://en.wikipedia.org/wiki/Extraterrestrial_liquid_water#Liquid_water_in_the_Solar_System) in our solar system with water, beyond the Earth. Europa is believed to have more than twice the water volume of Earth's oceans.
It is a non-believable old story trope that aliens want *our* water. Why not just grab a chunk from the Oort cloud? I read reciently that it looks like one of Jupiter's moons appears to have a bit more water than Earth's oceans. The most common elements in the universe are, in order, Hydrogen, Helium, and Oxygen. Water is ubiquitous.