The most common and effective way to test your reverse osmosis (RO) water, specifically the performance of your RO membrane, is by measuring and comparing the Total Dissolved Solids (TDS) levels of your tap water and the purified RO water.
Why Test Your RO Water?
Testing your RO water helps you ensure that your reverse osmosis system, particularly the crucial RO membrane, is working correctly. A properly functioning system should significantly reduce the amount of dissolved impurities found in your source water.
The Primary Method: Testing Total Dissolved Solids (TDS)
Reverse osmosis systems work by pushing water through a semi-permeable membrane that blocks most dissolved solids. Therefore, measuring TDS is a direct way to gauge how effectively the membrane is removing these substances.
Step-by-Step TDS Testing
Testing your RO water using the TDS method is straightforward:
- Obtain Samples: Collect a fresh sample of your tap water and a sample of the water produced by your RO system.
- Measure Tap Water TDS: Use a TDS meter (a small, handheld electronic device) to measure the TDS level of your tap water. Dip the probe into the tap water sample and note the reading.
- Measure RO Water TDS: Clean the meter probe according to the manufacturer's instructions (usually rinsing with RO water itself) and then measure the TDS level of your RO water sample. Note this reading.
- Compare the Readings: Compare the TDS reading of your RO water to that of your tap water.
According to best practices for testing your RO membrane, the RO water should be about 1/10 or less the reading of the tap water.
- In other words, if the tap water reads 250 ppm (parts per million), the reverse osmosis water should read around 25 ppm or less.
Understanding Your TDS Results
- Good Performance: If the RO water TDS is 1/10 or less of the tap water TDS, your membrane is likely working efficiently.
- Declining Performance: If the ratio is significantly higher (e.g., RO water TDS is 1/5 or 1/3 of tap water), it indicates the RO membrane's effectiveness is decreasing, and it may need replacement soon.
- Poor Performance: If the RO water TDS is close to the tap water TDS, the membrane has likely failed and needs immediate replacement.
What is a TDS Meter?
A TDS meter is an inexpensive and widely available tool that measures the electrical conductivity of water, which is directly related to the concentration of dissolved ions (solids) in the water. Readings are typically displayed in parts per million (ppm).
When Should You Test Your RO Water?
- After Installation: To establish a baseline for your new system.
- Periodically: Regular testing (e.g., every few months) helps monitor membrane performance over time.
- If Taste Changes: A change in the taste or odor of your RO water could indicate a problem with the system, including the membrane.
- Before/After Filter Changes: To confirm the system is functioning optimally after maintenance.
TDS Comparison Summary
| Water Source | Typical TDS Reading (Example) | Expected RO Water TDS (Comparison) | Performance Indicator |
|---|---|---|---|
| Tap Water | 250 ppm | - | Baseline |
| RO Water | 25 ppm or less | Approx. 1/10th or less of Tap TDS | Good Performance |
| RO Water | > 25 ppm | More than 1/10th of Tap TDS | Declining/Poor |
