Mechanical water filter for indefinite use? Does that even exist?

I've been in contact with a family in Africa for a little while now and they have asked if there was anything I could do to help them get by. I thought that a water filter would help, seeing as they don't have clean water, but I can't find one that can be used indefinitely. Most of them use carbon filters that need to be replaced every 26-200 gallons or so, and we're looking at roughly 10 gallons a day AND no access to electricity, does anyone know of ANYTHING that could work and that someone can actually buy?