Both phrases are idiomatic but they don't mean the same thing.
The difference between "water bottles" and "bottles of water" is the water.
Bottles of water have water in them.
Water bottles can be empty.
An empty water bottle is not a bottle of water, though it might be a bottle of air.
ell.stackexchange.com/users/24861/Lawrence
Yes, it's fine in everyday life.
For example, in this recent headline from Metro, the free London newspaper: Panic buyer screams at Tesco staff for refusing to let him buy 24 bottles of water https://metro.co.uk/2020/03/19/panic-buyer-screams-tesco-staff-refusing-let-buy-24-bottles-water-12424789/
ell.stackexchange.com/users/10161/richardb
You can see the same structure used with all sorts of English phrases,
e.g. Bottle of beer vs beer bottle Soda can vs can of soda Packet of crisps vs crisp packet Paint tin vs tin of paint If you say "water bottle" you're using "water" as an adjective to describe the type of bottle it is — a bottle (usually) used to store water.
So that could be a branded bottle (e.g. Evian) or a reusable bottle that people refill from a water cooler or tap.
If you say "bottle of water" you're putting emphasis on the state of things — there is some water in the bottle, (but you're not commenting on the type of bottle).
So you could say:
Can I put cooking oil in a water bottle? — Reddit: /r/NoStupidQuestions
This person is asking if they can put oil into a disposable bottle normally used for water (water bottle).
If they do, we could say it's a "bottle of oil" even though it's in a water bottle :)
ell.stackexchange.com/users/19442/anotherdave
A bottle of water is any bottle that currently contains water.
A water bottle is a bottle designed/intended to hold water .
If you get an empty Coke bottle and put water in it, it's a "bottle of water" but not a "water bottle".
Now people do reuse purchased bottles of water and those do get called water bottles, but if you say "water bottle" most people will usually think of a product purchased without water, usually made from heavy duty plastic or steel.
Photo by Amraepowell
ell.stackexchange.com/users/8790/curiousdannii
A bottle of water is a bottle with water in it.
A water bottle is a bottle that is used to hold water whether or not it contains water right now.
This applies to many containers that hold liquids: a teapot, a pot of tea; a paint bucket, a bucket of paint; a wine glass, a glass of wine.
ell.stackexchange.com/users/110585/Roger K Gabrielson
Agreed with Curiousdanii, but with one clarification.
A "water bottle" is always a multi-use item, not a single use plastic bottle.
Even when empty or when something else is in it, it's still a "water bottle" and is referred to as such.
Even is someone refilled a crinkly plastic single use bottle and is using it as a "water bottle", it's only obvious if you're pointing to it when you say "Hand me my water bottle.
"
Otherwise I'd look around for a metal or hard plastic one until they said, "that one there!".
A plastic bottle of water is usually referred to as "bottled water" (at least where I'm from) and is referred to that way "How much for a bottled water?", or can be "How much for a bottle of water?", but "How much for the water bottle?" is almost always said with trepidation referring to an overpriced contraption with special insulation or at least an easy open non-spill top.
ell.stackexchange.com/users/110622/Wayne
“Bottle of water” refers to the container and its contents.
“Water bottle” refers to the container.
ell.stackexchange.com/users/4451/MPW
A water bottle is a bottle for water[1].
A bottle of water is water in a bottle.
Bottle bottle bottle bottle bottle. -- [1] But not necessarily containing water.
ell.stackexchange.com/users/110708/onacosmicscale
Consider the following image.   In school, I was taught there are four "bottles of water". Do native English speakers say it that way in everyday life, or would it be better to say "four water bottles"?
Is the phrase "a bottle of water" something a native English speaker would say?
ell.stackexchange.com
<word-usage>
ell.stackexchange.com/questions/241205
ell.stackexchange.com/users/109190/WXJ96163
Bottles of water have water in them, water bottles can be empty.    e.g.   Bottle of beer vs beer bottle  Soda can vs can of soda  Packet of crisps vs crisp packet  Paint tin vs tin of paint   A  bottle of water  is any bottle that currently contains water whereas a  water bottle  is a bottle  designed/intended to hold water . If you say "water bottle" you're using "water" as an adjective to describe the  type  of bottle it is — a bottle (usually) used to store water.  Now people do reuse purchased bottles of water and those do get called water bottles, but if you say "water bottle" most people will usually think of a product purchased without water, usually made from heavy duty plastic or steel.     Water bottles are generally empty and can contain any fluid. However, bottles of water contain water and are full. 
Water bottles are generally empty and can contain any fluid. Bottles of water contain water and are full. 