With a proper functioning Reverse Osmosis system, the level of Total Dissolved Solids (TDS) of your R.O. water will normally be significantly less that of your tap water. A simple way to measure the TDS level is to use a conductivity meter. If your tap water is 400 parts per million and your R.O. water is initially 25 parts per million, you know that there is a problem with your R.O. system if your R.O. water suddenly registers 400 parts per million.
We sell this conductivity meter:
The AP-1: AquaPro (by HM Digital) costs $29 plus shipping. This meter has a one-year warranty.
To order a meter, please Click Here. For more info, please go to the HM Digital web site.