surely water has a high latent heat (meaning it sucks heat best) - but there is a little problem when it goes around in the engine, as the water circulates around it says hi to the radiator, then moves to the themostat guy who is actually a door guard and when finally it gets to the head and block it sees high temperature and also "shock"
This shock is a cool thing (fill a pateeli with water and tap it with a hammer) - the waves you see are cool aint they - the water also thinks they are cool - so it continues to party in the block and finally the pump pushes this water back to the radiator and the story repeats itself. The problem with this disco is that it also creates "implosions" which are reverse of explosions - these are high temperature bubbles which cause erosion (specially in iron block diesels) and each power stroke adds to it. This also happens when it gets high (spinning at high speed from the pump) and also cause cavitation there.
To keep it tame - we need to add some additives to the water to make it behave - meaning it can party all it wants and keep on sucking that good stuff (heat) but it should not harm others while doing so. So a few bits n bobs of chemistry stuff is added to it and also some oily stuff to keep the pump working.
Now we all now water will get really high like a kite from too much good stuff (heat) and sort of leave the ground - steam, - we need to control that as we need it to keep working even in high temperature - so we increase pressure in the system - but as we also have a recovery tank where the party is going on we add some alcohol to it - WOOOHOOO - solid party going on now. In this case the boiling point increases and it keeps on working without knowing it while H2O checks out the chicks in the "ol" pieces
We also know that water sort of expands like my neighbors wife - but only when cold, this is a problem because this expansion can create a hydraulic force that is capable of cracking metal castings - just like my neighbors chairs broke when his expanded wife sat on them. The same alcohol keeps this in check.
So to end the story.
we need water in the system to keep it working - but we know that the conditions inside will cause the water to party hard, cant help that - we need it to work. So give it a little dose of "stuff" to protect your assets (engine).