Wash a beaker with distilled water. Turn on the reverse osmosis system and let it run for 15 minutes.
Take a 2 ounce sample of untreated raw water from a valve at the inlet of the reverse osmosis system or from a raw water faucet in the system. Run this sample into the clean beaker.
Dip a TDS meter in the beaker. Press the "On" button. Wait a few seconds to let the meter analyze the TDS content. Record the TDS of the raw water in the notepad as RW-TDS1.
Wash the beaker with distilled water and take another 2 ounce sample of untreated raw water. Record RW-TDS2. Wash the beaker with distilled water and record RW-TDS3 in the same way.
Add RW-TDS1, RW-TDS2 and RW-TDS3. Divide the sum by 3 to get the mean raw water, called RW-TDS. This is the calculated mean, and is the final reading of RW-TDS. You can also find the final RW-TDS by using the concurrent reading method. Repeat the earlier procedure to get RW-TDS values until you get the same reading twice consecutively. This reading is called concurrent reading and can be considered the final RW-TDS instead of the calculated mean.
Wash the beaker with distilled water. Take a 2 ounce sample of treated water from the outlet of the reverse osmosis system or from a treated water faucet. Dip the TDS meter in the beaker and record the TDS of the treated water as TW-TDS1.
Repeat the procedure for recording TW-TDS2 and TW-TDS3. Find the mean of the three TW-TDS readings to get the final calculated mean TW-TDS reading. Alternately, find the final TW-TDS by using the concurrent reading method.
Record three pH readings for treated water using the same method. Use the pH meter to find TW-pH1, TW-pH2 and TW-pH3. Find the mean TW-pH reading.
Find the difference between the mean RW-TDS and TW-TDS readings. The amount of TDS reduced by the reverse osmosis system is the difference between the final RW-TDS and final TW-TDS. Reverse osmosis aims at removing 90 to 95 percent TDS. If the final RW-TDS reading is equal to or less than 3000 ppm and the final TW-TDS reading is equal to or less than 300 ppm (90 percent TDS reduction), it shows excellent performance of the system. A final TW-TDS reading of more than 300 ppm indicates poor performance.
Double-check your pH readings. A final TW-pH reading between 6.5 and 7.5 shows proper functioning of the system. TW-pH of more than 8.5 and less than 6.5 indicates improper operation. If you have readings in this range, you will need to replace the reverse osmosis membranes or the pressure pump.