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According to several articles from the American Water Works Association, permeate from RO should be stabilized in terms of pH and hardness to avoid corrosion of the distribution piping.
How does corrosion differ from that of normal water? Would RO water corrode stainless steel faster than normal water if both had the same chloride concentration?
Water passing RO does not have the same chloride concentration.
The raw RO water contains almost no ions, aside of those that passed by leakages of the osmotic membrane.
This disbalances the water natural $\ce{CO2/HCO3-}$ pH buffer, leaving the ionic alkaline buffer part before membrane, so water becomes more acidic with corrosion aggressive $\ce{CO2(aq)}$.
