Well, it certainly is not bad for you to drink icewater (unless you
have some special sensitivity, such as sensitive teeth. I had a friend
once who suffered asthma when he drank cold beverages).
What you may be asking about is whether the bottle may burst.
Plastic water bottles these days are designed so that their contents
may freeze without bursting the bottle (most of the time -- sometimes
the plastic is a little weak and you get a leak). Bottles are not
shaped spherically, but rather have indentations, lumps, bumps, and all
kinds of odd shapes to them. The water expands as it freezes, and the
bottle can deform as its volume needs to grow because the dents in the
bottle can pop out.
Bottles also have these shapes because you'd like them not to
burst when dropped. As one part of the bottle is crushed inwards on
impact with the ground, another part of the bottle must bulge out
because water isn't very compressible. Gallon jugs of milk have
circular dents in their sides for just this purpose. You can tell if
one's been dropped because its circular dents are popped outwards.
These features of plastic bottles don't always work, and you can
still end up with water or milk all over the place, but it happens less
often these days. Glass bottles are a real hazard.
(republished on 07/25/06)