Lewis Dartnell

rudimentary but perfectly adequate system for filtering out particles in murky lake or river water uses a tall receptacle such as a plastic bucket, a steel drum, or even a well-cleaned trash can. Punch some small holes in the bottom, and cover with a layer of charcoal, either taken from a hardware store or created yourself using the instructions . Alternate layers of fine sand and gravel on top of the charcoal. Pour the water into your receptacle, and as it drains through, it will be effectively filtered of most particulate matter.

Solar water disinfection, or SODIS

So if you were a survivor with an entire supermarket all to yourself, for how long could you subsist on its contents? Your best strategy would be to consume perishable goods for the first few weeks, and then turn to the dried pasta and rice, as well as the more resilient tuber vegetables, before finally resorting to the most reliable reserve of canned produce. Assuming also that you are careful to keep a balanced diet with the necessary intake of vitamins and fiber (the health supplements aisle will help you here), your body will need 2,000 to 3,000 calories a day, depending on your size, gender, and how active you are. A single average-size supermarket should be able to sustain you for around 55 years—63 if you eat the canned cat and dog food as well.