It is usually used to ...

It is usually used to increase effectiveness of disinfection, and not separately. Without coagulation the disinfectant is much less effective. Have you investigated slow sand for a really really low tech application? It still requires an operator with understanding of the process, but requires no special chemicals to enhance the effectiveness. I would only use it when other options were unavailable, but it can work. Combine slow sand with leaving bottles in an ultraviolet source (sunlight) in bottles that are permiable to UV and I would feel pretty good about an improvement of two or three orders of magnitude. But always test your product!