Waste water is MUCH cleaner than the water coming out of your tap! Consider that it's gone through all the prefilters.
Also consider this. If you take a glass of tap water and let it evaporate to 75% full, then drink that 3/4 full glass of water. Well, that's the equivalent to the "waste water". It's not waste water, it's just filtered water that didn't go thorugh the RO membrane. It takes with it the stuff that was in the 25% of the water that did make it through. BUt really the "higher concentration of ions" in the "waste" water won't harm you.
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