Keeping things like food and water refrigerated while you're camping in the bush is nearly impossible. Unless of course you've chosen to camp somewhere freezing cold. But if you haven't, evaporative cooling can be an effective technique to utilize for keeping water cool and food from spoiling as quickly. Obviously this can be crucial in a wilderness survival situation when your food supplies may be limited. This video outlines two ways to utilize evaporative cooling, first to cool a water bottle, and second to construct a small refrigerator-like hole in the ground where it can be as much as 20 degrees cooler than outside.