Why can't water be compressed?

Because there is not a lot of vacant space between the molecules of water. Oh, it is not just water either. Most liquids resist compression.
because water is.
water CAN be compressed. Why do you think it comes out of a faucet when you open the valve?
no space between molecules
It can. when evaporated. into cloud. and it can fall back down again as water:-)
See Ice, trick question
it can be compressed
i duno
Its a basic law of physical dynamics. You cannot displace matter, most things that can be compressed have a certain amount of air in them, which can be pushed out making it more dense. Water is as dense as it can be because it is a liquid.

It can be pressurized like the other people answered, but shocks on a car use the fact that water can be displaced but not compressed to make your car ride smoother. Hope that helps, you can look up thermodynamics of liquids to get a better understanding of how it all works.
Who said water can't be compressed? Liquids generally can't be compressed as much as gasses but if you have access to enough pressure you can pretty much do whatever you please.
The molecules in a liquid start to get in the way of each other eventually but if you start with a big push then you can work your way up to reducing the space required.
Perhaps you should have asked "Why can't most liquids be compressed"

No room between molecules to take up
Water can be compressed or pressurized. This is seen with a pressure washer. Water has many interesting qualities. Read the article below for some great information.
because it is a liquid. liquids cant be compressed, its one of thier properties.it only takes the shape of the container that it is put in.okay
The atomic spacing of water molecules is just about the same as in the solid state although without the long range order.
All molecules within a solid or liquid have an equilibrium spacing where attractive and repulsive electrostatic forces are in balance. As the material is compressed the molecules are moved closer together and this increases the electrostatic repulsive forces between them. This tries to restore the equilibrium spacing that existed prior to compression.
The greater the compressing force the greater is the restoring electrostatic force and so the volume change is negligible.
Water cannot be compressed because accoring to newton's third law of motion for every action there is an equal and opposite reaction and so the cohesive force between the water molecules are so high that if they are compressed by mechanical work the force given is just stored in it as potential energy and gives it out in the form of kinetic energy it is just conservation of energy
because the act of compression causes heat, and as you know, as the water gets hotter it will eventually turn to steam
Water CAN be compressed, just not very much relative to another fluid such as a gas. It has to do with the average kinetic energy of the molecules when in thermal equilibrium with the environment. The higher the average kinetic energy of each molecule, the more it vibrates. The more vibration, the further apart the molecules, The space between molecules determine the state, solid, liquid or gas. It also has to do with transferring electrons, and like charges repelling each other. A gas is very easily compress since the molecules are widely spaced and easily pushed closer together then they would be if left to themselves. A liquid is more closely ordered and has much less space between molecules, but still, there is rom to compress, it just takes much more force than air to squeeze out space between molecules. Even a solid will compress a fraction before it fractures under pressure. Funny thing about water, when you heat it, it boils, but if inside a rigid container, the pressure rises, as in a boiler, but it will stop boiling until you add more heat to start it boiling again. If you keep adding heat and letting the pressure rise, at a certain pressure and temperature which escapes me at the moment, the "critical point" the liquid/gas interface is undefined. Below that critical point, there is a clear separation of liquid and vapor.
because water is liquid ,its intermolecular space is less but still if we want to compress it , we have to apply extremly large pressure
Water is matter. if you observe air or gass cannt be compressed either nothing but nothing can.
if we keep on reducing the space for water (a constant quantity) then a time will come when the molecules are so close together that they donnt have much space between them. so we wont be able to compress it any further.

Hope this helps!!
it can-slightly
I have a hunch that you are asking this question with an internal combustable engine in mind? I've heard this brought up alot when it comes to auto engines, when they get water inside their engine cylinders, it wont compress like the fuel/air mixture did before, and the engine stops cycling. So yes, water can be compressed, but it definantly doesn't like it as much as other substances.

Just thought I'd add that in case you were thinking along those lines.
Easy answer - because it ca be compressed, but the forces involved are beyond the power of say you car engine, which is why it does pop if it gets lots of water in it.

Compression involves reducing the space between atoms (or molecules in this case) The electrons surrounding a nucleus are all negatively charge and hence reply repel the electrons surrounding the other nuclei, it is this force you need to overcome to compress something. In gases there is a bit gap between the atoms so it's easy to compress, in liquids the gap is much smaller so it's harder, and in solids the gap is small still and so it's even harder still, but you can technically compress something until its volume is zero and its density is infinite IE a black hole.
Haven't you ever ahd a wee - what, other than compressing the volume of water forces it out?

OK biologists, I know this is simplistic.
In which form? As a gas it can, as a liquid it can to form a solid (though water at 4C is denser than ice).
water can be compressed-imagine the pressure on the water in the sea four miles down-the higher the pressure on the water,the more 'cmpressed' it becomes!
Water can be compressed!
it is when its frozen. ICE
Funny how many answers confuse compression with pressurization. Water from a tap or a pressure washer is under pressure, sure, but it is not compressed - ie forced to take up less space. The reason why it can't be has been given by several posters.