WARNING:ONLY USE DISPOSABLE WATER BOTTLES! I'M NOT RESPONCIBLE FOR BROKEN NON-DISPOSABLE BOTTLES!!!
Step 1: Step One
First, Get an empty watter bottle. Easy enough.
Step 2: Step Two
Second, fill your watter bottle to the line that I put on my bottle. (You don't have to put the line on)
Step 3: Step Three
Freeze your bottle. I recomend leting it freeze over night for maximum coldness duration. (Pardon my french)
Step 4: (Alternate Step Three)
Freezing the bottle right side up is the easiest way to do it, but if you want a bottle that can stand upright, then I suggest freezing it upsidedown. (If you freeze it upright, the bottom of the bottle will push out, making it almost impossible to set down on a table or any surface for that matter)
Step 5: Step Four
If you froze the bottle upright, then skip ahead to the next step. If you froze it upsidedown, then try to manuver the chunk of ice out of the top so that it can move freely. (I use a screwdriver)
Step 6: Last Step
Just fill the rest of the bottle with water and you're done!