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'll revert to my old pessimistic self and say that there's nothing that can replace good ol' H2O.

Here are some things that a replacement liquid would have to do:

1. **Be denser as a liquid than a solid.** This is atypical of most substances, but water is an exception. This is why only the tops of ponds freeze over and the lower layers are frozen. Otherwise, nothing would survive in winter, because ice would form and sink down, letting more water freeze. Ice fishing would be much less interesting nonexistent.
2. **[Be the next universal solvent.](http://water.usgs.gov/edu/solvent.html)** If you've taken high school biology, then you might have heard the phrase "water is the universal solvent" a couple times. Water is good because it can dissolve quite a lot of things. A related pure-chemistry-inspired property is that water plays a huge role in the reactions of acids and bases.
3. **Stay liquid at room temperature, and the moderate ranges of temperatures seen on Earth.** If a substance is solid at 25 degrees Celsius, then we've got a problem (namely, the oceans). It must also be possible for this substance to be gaseous at some point, facilitating the water cycle.
4. **Be useable in both [cellular respiration](http://en.wikipedia.org/wiki/Cellular_respiration) and [photosynthesis](http://en.wikipedia.org/wiki/Photosynthesis).** The reasons for this are pretty straightforward. These are clearly not the only forms of energy production used by organisms on Earth (e..g thermophiles use different mechanisms), but they're what you'll have to use if you want things to stay normal.
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.