This is for sure a concern. Also when my RO system was first installed, the filter instruction said to run it to fully empty twice to run out the detergents (?) that the filters came with? I have to wonder what's in that, or lubricants used in construction.

I would not be surprised to find PFAs used somewhere in the construction of the system. Under regulation of this stuff means it's everywhere.

But then again, lots of the pipes, fixtures, etc. in the house ... plastic etc. as well.

Yeah the rubber bladder always concerned me as well. They say it is made of butyl so leaching is not to be expected but what if the production biproducts left on the inner surface are leaching out over time.

Same goes for a random o-ring or the PTFA tubing.

I have a TDS measurement device but these are questions beyond total dissolved solids.

I actually have a countertop RO system that puts the filtered water directly into a glass jar. The filtration system itself is certainly plastic.