It can get complex; let's say you use a cartridge stove, and you have fuel excess to your bare cooking needs. Your treatment times for the boiling of water - just bring to a boil and let cool - are much shorter than the treatment times for other techniques and you can make tea into the bargain, without bothering about pore size, clogging of filters, and other issues. I have used some pretty nasty water sources (e.g. Canyon de Chelly) without incident by boiling. It is simple and definitive.