It's not that hard to build a standard carbon filter. You just need some sand like from a river, plus some pebbles/gravel, and some charcoal from the bottom of a fire. You put all that into a clothe like an old shirt or something, from smallest grain to biggest, and put it in something to hold it, like an old bottle for a small filter for just yourself, or a bucket to filter more. It just naturally filters out a lot of crap out of the water. You can also just weave a mat with palm leaves or something like that to hold the charcoal and sand from going through. I would still suggest boiling after it goes through the filter, but it actually takes out quite a few bacteria. You can also bring it almost to boiling with the sun too pretty easily.

There are a ton of videos on YouTube that show you how to do this, as well as instructions on various sites, if they can manage to get access to the internet, or someone can to build something to help others.