We do have free water sources, just that none of them are clean enough for you to drink directly from it.. You will have to purify it someway, most probably by boiling it.

But then when you do that, you will need to put it in the fridge for it to get cold, which brings us to problem number two, lack of constant electricity to power your fridge.

So rather than go through all of that processes, most people prefer to just directly buy clean drinking water.