In a recent thread I posted -

"PP (polypropylene) has high tensile strength, making it ideal for use in caps and lids that have to hold tightly on to threaded openings. Because of its high melting point [266°F to 340°F], polypropylene can be hot-filled with products designed to cool in bottles."

Polypropylene is designated by the number '5' or 'PP' in the recycle triangle.
(1 liter soda bottles are typically #1.)

If the bottle's prior purpose was food related [and is a 5/PP] you should be fine.

Edited by greg23 on 07/08/2012 08:39:41 MDT.

I have one wide mouth Nalgene Cantene for that. (48oz)
Also polythilane .
I don't detect "taste" from that unlike from soda bottles and it takes only the space of the liquid inside.
The wide mouth makes it easier and safer to pour hot water in it.
Franco

My 12-oz. Kleen Kanteen triples as:

1. Hot water bottle
2. Extra water storage
3. Coffee/tea mug

Get the single-walled (not insulated/double-walled) kind and put a beer cozy around it to insulate it.

No plastic taste, no BPAs, no leaching of BPAs and other plastic chemicals into the water (which happens when you put very hot water in plastic), no leakage, and no shrinkage.

- Elizabeth