In the years we went to Mexico I used a Pura "whole house" filtration kit, it had 3 filter canisters, a trash filter followed by a fine charcoal filter and finally a UV light that operated off 12V. I mounted a 12V Shur Flo water pump before the Pura to boost the pressure so I could run directly into the coach. You do have to be careful with the pump though, in a campground I had the pump suck the hose closed (no flow from the water tap!). We had no issues with "Montezuma's Revenge" in the years we went into Mexico.