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.