Would it be possible to let RO water sit in them for a few weeks, then have the water tested, to see what changed? This might give you some idea if it'll kill ya or not.
What would you have them tested for? As the owner of a lab I can tell you that it would not take long to run up an expensive analysis bill if you don't know where to begin, analysis-wise.
They are great looking containers, but without knowing what was in them previously, it would be pretty risky to use them for holding anything that will be consumed.