it is not 0.018. As I said before, there aren't commercial TDS meters available with that kind of precision. My guess is, if you read the instructions that came with your TDS meter, you'll find that that is 18ppm.
In my opinion, 18ppm is too high. Flush your RO unit (ie, run the water so it doesn't go out the good water tube, it only goes out the waste tube) for several minutes, then collect a new sample and retest. If that doesn't fix it, it's possible that you need to replace the pre or post filters, or even the membrane itself.