I think you already know the answer you're going to get here.
I don't know that RODI is necessary for success, but it allows a measure of control over the primary component of out tank. Just picture where you live. If there was a coal power plant upwind from you, it is likely that you would have health issues. Mou may not keep over and die, but you would get more colds, be more susceptible to various diseases, etc.
I think clean water is key. Some have it, some need to filter. I live near the Marcellus Shale natural gas deposit, so we periodically hear about wells becoming contaminated with various byproducts of the industry. I have to admit, seeing water burn at room temperature is a bit unnerving.