It means two shots of water. A shot is a serving size equivalent to one ounce (about 30 cubic centimeters) . He wants two shots of Od Kentucky whiskey (that is why he said "double") mixed with two shots of water.

Thanks a lot!

Sorry, in my answer I said he wants the water mixed with the whiskey. He wants the water in a separate glass. He intends to drink the whiskey "straight" or "neat" meaning mixed with nothing and no ice. He will then drink the water.

也许是是水袋的意思？背在背上的水袋？你和上下文理解下看看对不对 0 0 。。。