I'm not sure what he does with coffee filters but they're near-universally recommended for the initial straining of water prior to sterilization. I'm aware of the fact that most of the people that include coffee filters have probably not tried them for that purpose; a few people say they don't work at all. I admit that some of my kits include them and I'm embarrassed to admit I've not tried them, either. I'm researching better pre-filters and waiting for better weather.