This is not a build, it hardly even qualifies as a recipe, but it's a great tip I use intensevily during the summer. Actually my father in law just mentioned it one day, so it might not be a revolutionary new idea, but a great idea none the less.
Note: In the summer heat, they do get quite wet on the outside, so please consider using a coaster if put on furniture.
Some claim that freezing water in plasticbottles, releases dioxin, and is therefore toxic.
Just as many claim it to be a hoax, or an urban myth.
Including this guy, witch to me looks pretty credible.
Please search the internet for info, and make up your own mind about this matter.
Step 1: Recycle.
Recycle your singleuse waterbottles, they're perfect for this. The more bottles you have, the longer it will be, before you have to 'reload' them.
Clean and rinse, proceed to Step 2.
Step 2: Just Add Water...
Now fill each one 1/3 - 1/2 with tap water.
The more water you add, the longer the cooling obviously will last.
Of course you will have less room for liquid water, but if you're near a tap, you just refill when empty, and wait a moment for it to cool.
Step 3: Freeze...
Put the bottles in your freezer, lieing down. This will get you the fastest cooling.
I guess if you freeze them standing, you will get slower cooling, but maybe over a longer period of time. I didn't test it.
Step 4: When Cooling's Needed.
Grab a frozen bottle from the freezer, maybe add a little flavor, and then fill up with tab water.
Wait a few minutes.....cold drink ready.
Step 5: Get Some Work Done.
Chopping through one foot of recycled concrete gravel, compressed by a 500 kg vibrator, does make one need a cool drink on a hot sunny day. (making flowerbeds, btw)