Water treatment for RV fresh water?

I have met a couple people who have UV homemade systems to purify water in Mexico. A more complex system provides a steady flow to the fresh water tank and then shuts off when the tank is full. An easy system can be built using sediment filters and carbon filters and one of the UV purifiers. Small RO systems can be built but require flushing. Good filters and a UV purifier should work. Here are a couple of related websites that provide info and parts. Many other websites provide the parts and filters. I found some suppliers have the UV systems but not replacement lamps which must be replaced each year. Also learned that UV will break down plastic so stainless steel would be preferred. If you have DIY talent you can build your own system for maybe $300.

http://www.waterfilteruniversity.com

http://www.h2osplashwaterfilters.com