How would we go about making charcoal suitable for use [with other materials] to filter water? Thanks.

For a simple three layer tripod filter of grass, charcoal and sand we were taught to use simple chunks of partially burned wood from thge cold fire pit. I believe you can mahe it by sealing chunks of wood in a sealed metal cannister and putting it in the fire. I have only read this and can't swear that it works. Hope this helps. SD

go to the aquarium store and buy a package of activated charcoal for the water filter

or as Snake_Doctor commented, heat wood (probably sawdust) in a closed container (with small hole to allow wood gas to escape),light the wood gas, when the wood gas no longer burns off, the char process is complete

keep in mind that charcoal from a fire has very little in the way of sites available to trap contaminants compared with so called activated charcoal which does.

if you insist on making your own charcoal based filter, buy it at the fish store.

ILBob is right about the enormous difference in adsorptive ability in regular vs. activated charcoal. We are talking orders of magnitude.

I make a lot of charcoal every year as a soil additive and (for the low grade stuff) outhouse use. I suppose a long column of powdered regular charcoal might be of use in improving odour and flavour, but when it comes to chemical removal its effectiveness would be open to question. Better than nothing, I suppose, but definitely not the first choice if commercial activated charcoal is available.

I need to research whether an off-the-shelf pressure cooker could reach the pressure/temperature required to convert regular charcoal into activated charcoal. Probably not, but it's an interesting idea.

I have read that you want to burn hardwood to an almost-white ash to boil to create lye; do you want to use the same type of wood to make filter charcoal?

Start with http://info.bioenergylists.org/

How to make high and low adsorption biochars for small research studies, by Hugh McLaughlin, PhD, PE, Alterna Biocarbon Inc.

All Biochars are Not Created Equal, and How to Tell Them Apart

description of making Activated carbon from Moringa husks and pods
1G Toucan TLUD for Characterizing Biochars, by Hugh McLaughlin, PhD, PE, November, 2009

handbook and video on Use of biochar in decentralized water treatment by Aqueous Solutions , Sustainable Decentralized Water Treatment for Rural and Developing Communities Using Gasifier Biochar

So you fill a 200 liter (55 gallon) oildrum TLUD with biomass, burn it , use the heat for cooking/drying/whatever, use the remaining charcoal as part of a filter

Awesome.

Thanks for the links, EMP_. This is an emerging field, and I'm greatly interested in ongoing research and development. I'll be giving those documents a close look.