I have 3 of these, they will keep your beverage cold all day in a hot car.

Thermos quick charge

I use a 1 liter water or soda bottle over and over and over again. Cheapest out of all that have been suggested so far and greener since you are recycling.

I used to do like Jim Tanker but freeze them if I wanted cold water on a hot day. They melt just about enough to give you a cold drink when you need one.
They also work as ice packs in a cooler if you use one.

I have a 100oz Thermobak and two 1 liter Sigg bottles with Neoprene covers. The Insulated Sigg bottles keep water about as cool as my Neoprene covered Nalgenes did. I believe the Camelbak keeps water cooler longer, but that is probably due to the amount of Ice I can fill it with.

I like the Polar Bottle, used it for years. Never had a problem. Plus it is insulated. As so like Nalgenes.
link for polar
http://www.polarbottle.com/

Desert bags always leak. Thats cool though.

"It's amazing what people have used"

Reminded me of a time I was finishing up a week long backpack in the Grand Canyon. I was on the Bright Angel Trail, hiking up from Phantom Ranch. Guy coming down the trail carrying (in hand) a 1 gallon plastic container like you would buy milk in. It appeared to have Gatorade/Koolaid/ or something. He seemed to be just as happy as a clam on a rim to river to rim hike.

LW

At one of the various primitive skills courses I've taken over the years, an assistant used a dried gourd with a corncob stopper on a sling of cordage she made from dogbane...

Eco friendly means no truck delivered, plastic stored, bottled water. Tap water is the way to go
Cheers

One thing people overlook with military canteens and canteen holders-the fuzzy stuff inside is INSULATION. While in Cuba, we would chill our canteens, then soak the holders in cool water, and it would keep the contents cold most of the day. A wool sock would likely do the same over a bottle-we used to soak our berets as well, and that works great too. I dont think, side by side, there would really be any difference between an uninsulated plastic bottle vs an uninsulated metal one. Metal conducts heat better though, so it MAY be plastic works better-but, again, I think for the sake of argument, the difference is negligible.
I agree with Colorama too...tap water is fine here in the US. I refuse to purchase water when I get the same stuff for free. Save your money for something that ISNT given to you....