Question about 20ppm

After reverse osmosis im left with 20ppm. What is in that ppm? some calcium?

Hard to say without having it tested. Just curious what was it before the RO?

The hydrologic RO system I bought came with a water saver option. you could put this thing in line and it would waste much less water than hitting the 0 ppm mark. Sure the water came in at more than 0 ppm. Still 20 ppm is low.
The benefit, there isn't 4 times the waste water as the 0 ppm water.