Any such evidence would need to be placed into context and therefore would be difficult to evaluate. In other words, an apples to apples comparison would be tough to achieve.
Before we even start discussing RV tank residence times, the variables impacting initial tank water quality (at the point where it is put into the RV) include but are not limited to:
- The source utility itself (how it is being run both administratively and in terms of engineering; how old is it, etc.)
- Whether the source utility is using surface water, ground water, or a combination of the two (each has its own disinfection challenges).
- Disinfection methods used by the utility (which may be partially influenced by its size)
- Geography (south tends to have greater biological intensity)
- Population served by the utility (which can influence distance from the disinfection source, which can influence chlorine residuals)
- Season (summer = microbes multiply more quickly)
- Prevailing weather (turbulence can amplify surface water disinfection challenges)
- At what location in any given water distribution system a Class B tank was filled, because initial system residence time for the origination water will have a big impact on what happens in the Class B tank from that point forward.
- How the Class B tank was managed historically (our previous owner apparently filled ours with lake water, which deposited a residue which gave me several years' worth of bacteriological problems despite ongoing flushings and re-chlorinations).
It goes on and on. You can read anecdotal reports of how longer water residence times are correlated with larger number of trips to the emergency room for GI infections (e.g.,
here) - and that's for dynamic public water systems, not for static water residing in tanks. But beyond that kind of level of analysis, it's difficult to quantify.
Texas has regulated drinking water disinfection since 1947. Free chlorine minimum is currently set at 0.2 mg/L.