Well, you’ve remembered to pop a bottle of water in the freezer the night before you head to the local park to top up your tan. You slap on your sunblock, put on your sunglasses and head to the freezer to get your bottle of ice before leaving the house.
10 minutes in and you’re already sweltering from the sun in the cloudless sky so you reach for your bottle only to find it’s still a block of ice! So you resort to holding it to your head in a vain attempt to cool down while enviously watching others swigging from their already-melted bottles of ice.
This is what you should have done: fill the bottle with water half way up, then lie it on its side in the freezer. When you retrieve it the next day, it will have frozen on one side so all you have to do is fill the rest of the bottle with water or diluted cordial.
Et voilà you can enjoy an ice cold drink whenever you want!