Advanced TDS Calculation Using RO System
Formula Used
The calculator uses common RO performance formulas. TDS values are entered in ppm. Volume values are entered in liters.
| Calculation | Formula | Meaning |
|---|---|---|
| Rejection Rate | ((Feed TDS - Product TDS) / Feed TDS) × 100 |
Shows how much dissolved material the membrane rejects. |
| Passage Rate | (Product TDS / Feed TDS) × 100 |
Shows how much dissolved material passes through the membrane. |
| Recovery Rate | (Product Volume / Feed Volume) × 100 |
Shows the percent of feed water turned into product water. |
| Waste Ratio | Waste Volume / Product Volume |
Shows how many liters go to drain per liter produced. |
| Final Blend TDS | ((Product TDS × Product Volume) + (Feed TDS × Bypass Volume)) / Total Volume |
Estimates final TDS after bypass or remineralized blending. |
| Salt Load | TDS × Volume / 1000 |
Converts dissolved solids into estimated grams. |
How to Use This Calculator
- Measure raw feed water TDS with a clean TDS meter.
- Measure membrane product water before any remineralizer if possible.
- Enter final drinking TDS if your system adds minerals after filtration.
- Add feed, product, and waste volumes from a timed collection test.
- Enter pressure, hardness, chlorine, pH, and membrane age for better notes.
- Press the calculate button and review the result above the form.
- Download CSV or PDF records for future maintenance tracking.
Example Data Table
| Case | Feed TDS | Product TDS | Feed Volume | Product Volume | Waste Volume | Rejection | Recovery |
|---|---|---|---|---|---|---|---|
| New membrane | 500 ppm | 20 ppm | 10 L | 3 L | 7 L | 96.00% | 30.00% |
| Normal use | 650 ppm | 45 ppm | 12 L | 4 L | 8 L | 93.08% | 33.33% |
| Needs review | 700 ppm | 180 ppm | 10 L | 5 L | 5 L | 74.29% | 50.00% |
TDS Calculation for RO Systems
What TDS Means
Total dissolved solids, or TDS, shows the amount of dissolved material in water. It is measured in parts per million. A reverse osmosis system lowers TDS by forcing water through a semi permeable membrane. Clean product water passes through. Most dissolved salts move to the drain stream.
Why RO Performance Matters
This calculator estimates key RO performance values. It compares feed water TDS with product water TDS. It also checks rejection rate, passage rate, recovery rate, waste ratio, and estimated brine strength. These values help you see how well the membrane is working.
A high rejection rate means the membrane is removing minerals well. A low rejection rate can point to membrane wear, poor pressure, chlorine damage, bad seals, or sampling errors. Recovery rate shows how much feed water becomes usable product water. Very high recovery can raise brine TDS and scaling risk.
How to Read Results
The tool also estimates salt mass in each stream. This is useful when you want to compare quality and efficiency. For example, a feed TDS of 500 ppm and product TDS of 25 ppm gives a rejection rate of 95 percent. That is often a strong result for household RO systems.
Testing Tips
Use fresh samples for better accuracy. Rinse the TDS meter probe before each reading. Test feed water before the prefilters if possible. Test product water after tank flushing. If your unit has a remineralizer, test before and after it to understand the added minerals.
Maintenance Guidance
Results should guide maintenance, not replace lab testing. TDS does not identify every contaminant. It also cannot confirm microbiological safety. However, it is a quick way to track membrane performance over time.
Record results monthly. Watch for trends instead of one reading. If product TDS rises suddenly, inspect filters, pressure, tank condition, and membrane seating. Replace parts based on manufacturer advice and local water conditions. For best records, keep the same testing method every time. Measure water temperature, because meters can drift when samples are very cold or warm. Note filter age, pressure, and tank status. These details make troubleshooting faster and more reliable for users.
FAQs
What is TDS in RO water?
TDS means total dissolved solids. It estimates dissolved minerals, salts, and metals in water. A lower number after RO filtration usually means the membrane is reducing dissolved material effectively.
What is a good RO rejection rate?
Many household RO membranes perform well when rejection is above 90 percent. A result above 95 percent is often strong. Always compare results with your membrane rating.
Why is product TDS rising?
Rising product TDS can come from membrane wear, low pressure, damaged seals, chlorine exposure, scaling, or a poor sample. Test again before replacing parts.
Does low TDS mean water is safe?
Low TDS does not confirm full safety. TDS meters cannot identify bacteria, many chemicals, or every contaminant. Use proper lab testing when safety is uncertain.
Why does remineralized water show higher TDS?
A remineralizer adds minerals after filtration. This can raise final TDS while the membrane still works correctly. Test before and after remineralizing to compare both readings.
How often should I test RO TDS?
Monthly testing is useful for most homes. Test more often if taste changes, production slows, feed water varies, or filters are near replacement time.
What causes high waste TDS?
Waste water carries rejected dissolved solids. High waste TDS can be normal, especially when recovery is high. Scaling risk may rise when brine becomes too concentrated.
Can this calculator replace professional testing?
No. It estimates RO performance from TDS and volume readings. Use certified laboratory testing for health, microbiology, heavy metals, and regulated contaminant checks.