--- I just wanted to share some thoughts and open a discussion on this topic.
I've owned or leased any number of RV's over the years, most of which came with the fresh water system already on board. For my '46 Shorty, I am building it from scratch and hope to apply what I've learned and whatever you folks might want to contribute. My biggest peeves with all the built in systems was that the typical polyethylene (white translucent plastic) tanks...A.) make the water taste funky and "plasitcy"...and B.)...are prone to mold & algae growth...and C.) rarely if ever have any baffling.
This time, I plan on using interior mounted ABS (a black plastic) tanks as they impart no unwanted flavor to the water, are baffled and are algae & mold resistant. The only ones that seem to be on the market unless you spend big bucks to have one custom made are from Valterra and are limited to certain dimensions. They are all 8" x 16" x whatever length which can make for limited applications. In my case, I will be using three 12 gallon tanks conjoined to yield a 36 gallon system. Plenty for my solo use.
ABS Water Tanks Archives - Valterra.com | Valterra.com
The ABS is also much easier to work with in that you can use ABS cement to install hose connections and such where the polyethylene can only be "spin welded" and the joints are commonly prone to leaking if not professionally installed.
I have my "City Water" and "Gravity Fill" inlets which will both have inline filters and will back them up with another pre-pump filter. There are a host of other fancier filters, but I believe I can get by with these since the majority of my drinking water will very likely be bottled and hope to only occasionally rely on local city water for that purpose since it varies so greatly around the country in terms of quality.
Mind you, this will be a very simple system consisting of a single kitchen sink, a hand-held shower and one outdoor connection (very handy for cleaning off muddy boots or whatever else you don't want to drag inside). The internal & any external plumbing will all be PEX lines which also does not impart taste and has a good measure of freeze resistance. I am still shopping water heaters but leaning towards a tankless unit since they conserve a great deal of propane. I am even thinking about having a second, electric water heater for the occasions when I might have the necessary 110v hook up such as you find at RV parks and some campgrounds. That would free up extra propane for cooking (I still prefer fire for that..it's a primal thing).
I welcome any ideas, thoughts or plans you all might have regarding this very basic need.