Delrin is a homopolymer acetal, and was actually invented by Dupont. To my knowledge, GE doesn't manufacture an acetal at all. Celcon is another Dupont name you may run across, which is an acetal copolymer and in general, much easier to deal with than the homopolymer.
Acetal is generally used because of it's abrasion resistance, it's VERY tough, although the impact properties fall far below polycarbonate. You'll find it used in plastic pulleys, etc. It's also relatively "slick" so it makes a good plastic bushing/bearing. It's not good for outdoor use without due to it's weatherability and the fact that it's hygroscopic (absorbs water from the atmosphere).
As you suggested earlier, polycarbonate is definitely the way to go for the "taste" properties. The drawback being that it's not extremely flexible so you won't be able to squeeze the bottle. You should be able to use them for 3-4 years before ultraviolet light takes its toll...longer if stabilized. Polycarbonate is the material used to make bullet-proof glass, it's probably one of the strongest polymers available.
I suspect the best "all-around" polymer for water bottles to be polyethylene, preferably a very opaque white (will stay cooler to some degree, and protect the contents better by reflecting light). If you remember the yellow milkjug craze starting...the yellow was picked because it blocks almost all light in the blue part of the spectrum. Blue light is one of the main things that causes milk to spoil. By making the jug yellow, they in a sense increased the usable life-span of a gallon of milk. When all the cartons were cardboard, this was a non-issue to some extent since they were 100% opaque. Although cardboard introduced it's on "taste". The only real trade-off of polyethylene would be it's life-span since it's going to tend to pick up the taste. That can probably be avoided as long as ithe drink doesn't sit in it for days at a time. Something like coffee on the other hand, will probably stain it on the first use and be very difficult to clean.
In the end it's a trade off, polycarbonate is much more durable and taste resistance, but you give up the "squeeze" aspect of polyethylene bottles.
John