Western Style 4 Quart Round Canteen

Four quarts of water, Western Chic. 

Comes with a sling strap (it sucks, too small, bad nylon) -- but it's serviceable and you can always loop another strap on through.  

High impact plastic body, lined with metal and faux wool, this is a great supplementation to your smaller one and two quart canteens.  Would probably just throw this in the ruck up high and next to the body to carry water for when you get to camp.