I was collecting rainwater, and I live near a clear stream, which got me thinking. The foundation of human civilization is agriculture, namely grains, allowing us to form sedentary societies. Wheat, rice, corn. The cornerstone of agriculture is water, and clean drinking quality water is critical to life, cooking, hygiene, and survival. If you have water, you can sustain human life, and secure food and everything else necessary to human society. Even before civilization, humans spent most of their existence in tribal societies, where water was still crucial.

We can filter contaminated water, from the surface, from rainwater, or from underground. Clear fresh water from the wilderness can be boiled or treated with iodine in a survival context, but a simple three stage filter can produce purified water. The main components you need to create a survival water filter are gravel, sand, and charcoal. You can get these from the wilderness, and charcoal from burning wood of course in a campfire or charcoal making stove. A small filter can be made with a 2 liter bottle, which works very well, but a bucket filter can purify a large amount of water for storage. Eventually, the filter material will be replaced, so you can make a refillable one or three bucket filter for extremely cheap if you source your own filter material.

The result is clear, pure water directly from nature that can then be boiled or even distilled on a campfire if you'd really like.