Well, that depends on what you mean
by "taking water to space." Do you mean in a
spaceship? That is, is the water exposed to
vacuum or not? Let's talk about each case
If the water were exposed to the vacuum of
space, it would instantly begin to boil. That's
because the molecules in the water are
constantly jiggling around - if the water is
exposed to air, some molecules move from the
water into the air, but some water molecules in
the air move back into the water, leaving the
water in equilibrium with the air. In vacuum,
however, any water molecules that leave the
water just float away, so the water evaporates.
If the water is weightless, the lack of any
pressure makes this evaporation happen
throughout the water (and not just on the
surface), making it boil. Eventually, this
boiling would remove enough heat from the water
that some of it would freeze into a chunk of
ice. In this case, the density of the water
vapor will be much lower than the density of the
liquid water (in fact, as water vapor spreads
out into the vacuum, its density goes to zero).
The density of the ice would be a bit less than
the density of the liquid water, too, since ice
is less dense than water.
If instead the water is exposed to air but
were weightless (as it would be in, say, an
orbiting spaceship), then the density of the
water would be pretty much the same as it would
be on the surface of the earth. Technically,
that's not quite true - on the surface of the
earth, a glass of water has weight, and that
weight "squishes" the water a little bit. The
amount of "squishing" is what we call the
compressibility of water. In a weightless
environment, this squishing wouldn't occur, and
the water would be slightly less dense.
However, the compressibility of water is very
low, which means that the water doesn't squish
very much under its own weight; as a result, its
density in space would be more or less the same
as on earth.
I hope this helps to answer your question!
Liquid water, being liquid, would not
appreciably change density if moved into a
vacuum. However, there is no temperature at
which liquid water is stable in a vacuum, so it
would immediately begin to boil and escape into
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