To test your water for Total Dissolved Solids (TDS), you will need water samples (2 tablespoons each) of both your tap water and your Reverse Osmosis water. However, in order to get an adequate sample of your R.O. water, you should first turn off your tank. Then let the water drip out of the faucet for ten minutes to flush your filters, membrane, and tubes. Then take your samples. (Make sure your containers are clean.)

Once you get the samples, there are various ways to test them:

- bring samples of your R.O. and tap water into a local water store.
- mail two plastic bottles to us, one with one ounce of your R.O. water and the other with one ounce of your tap water -- we will test it for free and let you know the results.
- purchase your own conductivity meter.

Note that once you know the TDS of your tap water, you don't have to send it in for testing anymore -- just your R.O. water.