Water is life.

This topic brought to you by the ridiculous amounts of rain on my campus and the discovery of my long lost umbrella. Now if only I could locate my raincoat...

*Ahem.* I am tired of answering the water question repeatedly, so I am putting a full explanation up here for your reference. Please note that it is founded in science, not science fiction. Do with it what you will.

Calli's Axioms for basic Thrive Chemistry:
1) Water is LAWK. Life as we know it requires water for a variety of reasons. If you can come up with a type of life that does not require water (and I am not talking about water substitutes, which are not the same thing and do not help us) then you can do the physics and chemistry involved to keep that organism alive. Just don't expect the organism to be anything resembling LAWK, even down to the replication of DNA.
2) Water is always H2O. There are all sorts of things that you can dissolve in water, to make the solution salty, acidic, basic, or just plain ionic, but the chemical formula for pure water is aways H2O. Not only does basic nuclear physics make the hypothetical derivatives such as H3O and H4O impossible, the unique chemical properties of water are all necessary for LAWK, even basic cells.

These unique properties are as follows:
1)The Universal Solvent Dissolves Your Belgium. Pretty much everything with any charge or polarity will dissolve in water. This makes it a great medium for carrying around basic sugars, which happen to be cell food, and also those funny sugar chains, which form those long strands known as DNA and RNA. Water found in nature is almost never pure, containing Ions of all descriptions, which allow it to conduct electrical charges. This is very important if you are an electric eel. Also if you happen to be standing in a metal bathtub in a thunderstorm.
2)Unique Polarity Structure. The same polarity structure that enables the above also just happens to create surface tension. Merriam-Webster's medical dictionary defines surface tension as: [quote=Merriam-Webster]the attractive force exerted upon the surface molecules of a liquid by the molecules beneath that tends to draw the surface molecules into the bulk of the liquid and makes the liquid assume the shape having the least surface area. [/quote]
Basically, it allows water to stick to surfaces, slows evaporation, and allows all sorts of inter-cellular properties such as our cell walls. If it had no surface tension, it could probably slip between the phospholipid layer a heck of a lot more easily.
3)Ice is less dense than water. Since ice and snow are less dense and have air pockets, they make good insulators. Also, the fact that they float on their liquid counterparts enables a) Icebergs, Iced Lemonade, the Polar Caps and b) life to live in water in temperate climates in the winter. If Ice sank, life would be crushed. Literally.
4)The three phases can be found within a relatively narrow range of temperatures, but not so narrow of a range that you hardly ever get more than one phase.
Water's freezing point is 0 celsius (that's 273 Kelvin) and it's boiling point is 100 degrees celsius, (373 Kelvin.) By contrast, the boiling and freezing points of Iron are over 1,000 Celsius or Kelvin apart. (1535 C / 1808 K and 2862 C / 3135 K, respectively.) For anothe example, nitrogen melts at 63.15 K (-210.00 °C / -346.00 °F) and boils at 77.36 K (-195.79 °C / -320.3342 °F.) This is a really small range, just over 10 C/K, which is why we don't see liquid nitrogen pooling in our city streets. Also, liquid nitrogen is freaking cold and you should not stick your unprotected hands in it. Anyone who claims to be doing so is either a) an idiot or b) really using dry ice.
Being able to find all three phases in a decent range of temperatures means that water, that valuable life-giving compound, can travel. Also that it can take stuff with it - bringing particles down out of the atmosphere when it precipitates, washing soil into streams, freezing wooly mammoths in the depths of permafrost for the enlightenment of sentient beings...

I've waxed philosophical about chemistry for long enough. It's enough to know that when you discover a chemical with every single unique chemical property of water, you will then be permitted to talk about water substitutes. Until then, I, as disgruntled forum chemist, respectfully ask that all "waterless life" talk be deferred to the hypothetical until some one does the chemistry.

This is the formal list of water chemistry guidelines, otherwise known as Belgium that Dissolves in Water and Belgium that Doesn't. Double posting for your convenience, and to not eat your browser much. Also, this will get edited as I do research, and the above won't.

Belgium that Dissolves in Water:
Rules:
1) Polar solids will dissolve. Eventually.
- Polar solids include ionic salts, which dissolve easily, and covalently-bonded structures, which will eventually break into their constituent mollecules. Usually more work is needed to break the molecules themselves.
- Sometimes dissolving takes work, such as the addition of energy, but you will be able to force a solution, rather than an emulsion.
2) The larger it is, the harder it is to dissolve. There is a point at which it will dissolve, but not stay in the water, because it's too darn dense.

Belgium that Doesn't Dissolve in Water:
1) Things that are non-polar. There are exceptions to this rule, and they will end up stuffed in the more specific list of Belgium that Dissolves as I run across them.
2) Specifically, nonpolar hydrocarbons, including but not limited to the large majority of those that you would find in an oil well. Oil and water don't mix. Lipids and water don't mix.
3) Stuff with ridiculously strong inter-molecular forces or just plain complicated bonds. In the running are metals, diamonds, etc. At this point, I don't care if they're polar, because they get their own special rules that are stronger than mere polarity and keep them together.

One of the most useful threads. Period.

Someone should sticky this.

Thank you for creating this. Something that I think deserves a mention is that there is, and I have checked this fact, no known non-metal compound that has a solid that floats on it's liquid. None. So unless we want life that has never heard of the idea of living in a pond all year, alternate compounds for water ARE IMPOSSIBLE.

I'd sticky, but it seems only ADMIN can sticky stuff.

yes this is EXTREMELY important because i watched science programs and they said that if water was not "different" there wouldn't be any life on earth. i mean by different is the unique properties water has one major one being that waters solid is less dense then its liquid form. also does this mean were going to make water the default liquid that life crawls out of?

Gracias a todos. (Forgive me, I just came from spanish class.)

Yes. Water is default liquid, and we can play with what's dissolved in it later. This does not mean don't make liquid methane biomes, but they're going to need a seperate classification system (all of our current biomes are linked to be possible on the same planet) and they will all be at sucession stage 0.

A Possion - which metal compound floats on it's liquid? Is it tin or aluminum? Or is it one of those special ultralite airplane ones? (The boiling point of metal is extrordinarily far above sterilization temperatures, before anyone gets ideas.)

WRONG! Mercury is a liquid metal at room temperature. *poke, poke*