Earlier quoted context omitted.
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Can be purified. Activated charcoal filters are not the most efficient solution, but work reasonably well and can be easily built in an off-grid environment
> In physical activation, wood, coal, or any regular carbon source is first heated up to 600 to 900 degrees Celsius (1000 to 1600 degrees Fahrenheit) in a chamber filled with inert gas. The inert gas ensures that the carbon doesn’t burn. Instead, as the carbon is heated, any impurities left on it are vaporized and removed, leaving nothing but pure carbon.
> Next, the pure carbon is exposed to oxygen or steam baths at even higher temperatures. This causes the carbon to fracture and form the fractal shapes with their extremely large total surface area.
> In chemical activation, raw carbon sources are mixed with an acid, base, or a salt. The mixture is then heated. Chemical activation takes less heat and less time to achieve the end result, which makes it the method of choice for large scale activation.
Doesn't look "easily" to me but that's the first link google showed me (https://www.thinkcrucial.com/blogs/blog/how-activated-charco...)
What bothers me though is that our environment is changing so much and so fast that homo sapiens could not emerge tomorrow like they did first. No way a primate without culture or science is going to regularly scramble a charcoal filter to drink water.