They're not being asked to install flush toilets, just a better holding system so that runoff can't wash the raw waste into the water supply. A lined hole in the ground, basically. Adding lime isn't "modern". My Grandpa did so back at the turn of the 20th century, and he'd learned from his family. They didn't know then that it actually works to bind bacterial agents, they just knew it made the outhouse smell better.
I'm really unsympathetic to their problems with this. My advice to them is to go shit in their own water source and see how they like it.
This is Sanitization 101. It's been going on for thousands of years and if that's not good enough for them, then they can contaminate their own water supply and then treat the resulting diseases.