is quite wasteful of water. How it works is that it uses pressure to force SOME pure (more or less) water pass a semi-permeable membrane to get your finished water. The rest of the water is dumped out.
And you cannot reuse that waste water. When you remove the pure water from your source, the ions in the remaining water gets concentrated. <That is why the KH
increases in your waste water.> The RO
unit can only handle a certain concentration gradient across the membrane, so it can't push any more pure water out of the waste. <Even though the waste water isn't that concentrated.>
If it will help, you might use the waste water to water your lawn or something rather than flushing it down the drain.