I always use the concentrated stuff straight in the winter, not only prevents the bottle from freezing but will usually keep your nozzles working too - in summer (ok, in warmer weather) I have never found anything better than Clearalex for nice clear glass.
Clearalex comes in a small sachet (I used to get it at Esso stations) but it is getting more difficult to find. One small satchet will be enough for most water bottles and in winter you can add up to 25% meths for anti-freeze.
There is another additive very similar to Clearalex which also comes in small satchets, but it's not as good - can't remember it's name.