I think the only feasible ...

I think the only feasible low cost solution is solar distillation. There are very different methods that you can easily find in the web (from very low cost solutions made by plastic sheets, to integrated plants that produce distilled water and electricity). It can be applied both at household and community level. The only you need is the sun. So it fits well in hot, dry climates.

With respect to the arsenic content, I understand that there are succesfully attempts to remove arsenic from water using solar distillation. See for example:

http://www.watertechonline.com/arsenic-the-great-chameleon/

https://novascotia.ca/nse/water/arsenicremovaldistill.asp

Good luck

Giacomo