Buying or maintaining a reverse osmosis (RO) system can feel overwhelming. You’ll hear words like TDS, pre-filter, membrane, or flow restrictor and wonder what they actually mean. The truth is, understanding these terms is not just for technicians—it’s for anyone who wants safe drinking water at home or in the workplace.
This guide explains the most common RO terms you should know, breaking them into simple explanations. By the end, you’ll be able to understand your purifier’s manual, communicate with service providers, and even troubleshoot basic issues on your own.
Key Takeaways
- RO systems have their own terminology, covering filters, membranes, pumps, and water quality terms.
- Knowing these terms helps you maintain your system properly.
- Some terms like TDS, PSI, and micron rating determine how efficient your RO purifier is.
- The glossary covers components, process stages, and water quality measures.
What Are the Most Common RO Terms?
Here’s a list of terms we’ll cover:
| Category | Key Terms |
|---|---|
| Filters & Membranes | Sediment Filter, Carbon Filter, RO Membrane, UF, UV |
| System Parts | Booster Pump, Flow Restrictor, Check Valve, Storage Tank |
| Water Quality | TDS, PPM, Micron Rating, Rejection Rate |
| Operations | Permeate, Concentrate (Reject Water), Recovery Ratio |
| Maintenance | Flush Valve, Pre-Treatment, Post-Filter |
Now let’s break them down.
Filters & Membrane Terms
1. What Is a Sediment Filter?
A sediment filter traps dust, sand, rust, and visible dirt before water enters the RO membrane.
- Typical rating: 5 microns.
- Protects the delicate RO membrane.
2. What Is a Carbon Filter?
A carbon filter removes chlorine, pesticides, and chemicals that cause bad taste or odor.
- Two types: Granular Activated Carbon (GAC) and Carbon Block.
- Essential because chlorine damages the RO membrane.
3. What Is an RO Membrane?
The RO membrane is the heart of the system.
- Pore size: 0.0001 microns.
- Removes dissolved salts, heavy metals, nitrates, and fluoride.
- Purification efficiency: up to 99%【WHO, 2022】.
4. What Is a UF Membrane?
Ultrafiltration (UF) uses a 0.01-micron membrane.
- Blocks bacteria, cysts, and suspended solids.
- Works without electricity.
- Does not remove dissolved salts.
5. What Is a UV Filter?
A Ultraviolet (UV) filter uses UV light to kill bacteria and viruses.
- Works as an additional layer of safety.
- Common in areas with microbial contamination.
System Parts
6. What Is a Booster Pump?
RO membranes need high pressure to function. A booster pump increases water pressure to 50–100 PSI.
- Without it, RO purification slows down.
- Essential in areas with low water pressure.
7. What Is a Flow Restrictor?
A flow restrictor controls the flow of water through the RO membrane.
- Maintains pressure balance.
- Prevents excess water from bypassing the membrane.
8. What Is a Check Valve?
A check valve prevents purified water from flowing back into the RO membrane.
- Protects the system from contamination.
9. What Is a Storage Tank?
Since RO is slow, purified water is stored in a pressurized storage tank.
- Capacity: 5–10 liters in domestic units.
- Ensures on-demand availability.
Water Quality Terms
10. What Is TDS?
TDS (Total Dissolved Solids) measures salts, minerals, and impurities in water.
- Expressed in ppm (parts per million).
- Ideal drinking water TDS: 150–300 ppm.
- Above 500 ppm: not recommended by WHO【WHO, 2022】.
11. What Does PPM Mean?
PPM (parts per million) is the unit for measuring TDS.
- Example: 200 ppm = 200 milligrams of dissolved solids in one liter of water.
12. What Is a Micron Rating?
A micron rating shows the size of particles a filter can block.
- 5 microns: removes dirt and rust.
- 1 micron: removes fine particles and some cysts.
- 0.0001 microns: RO membrane (removes salts and viruses).
13. What Is Rejection Rate?
The rejection rate tells how much impurity the RO membrane removes.
- Example: If raw water has 500 ppm and purified water has 50 ppm, rejection rate = 90%.
- Higher rejection = better performance.
Operational Terms
14. What Is Permeate?
Permeate is the purified water that passes through the RO membrane.
- Safe to drink.
- Stored in the tank.
15. What Is Concentrate (Reject Water)?
The concentrate or reject water is the waste stream that contains dissolved salts and impurities.
- For every 1 liter of purified water, 2–3 liters may be rejected.
- Can be reused for cleaning or gardening.
16. What Is Recovery Ratio?
The recovery ratio is the percentage of feed water converted into purified water.
- Domestic RO: 25–35%.
- Industrial RO: up to 75%.
Maintenance Terms
17. What Is a Flush Valve?
A flush valve periodically flushes high-pressure water through the RO membrane.
- Prevents clogging.
- Extends membrane life.
18. What Is Pre-Treatment?
Pre-treatment includes filters and processes used before the RO membrane.
- Examples: sediment filter, carbon filter, softener.
- Essential to protect the RO membrane.
19. What Is a Post-Filter?
A post-carbon filter (also called polishing filter) is the last stage.
- Improves taste and odor.
- Ensures water is pleasant to drink.
Extra Terms You Might Hear
20. What Is a TDS Controller?
A TDS controller mixes some raw water with RO water.
- Restores essential minerals.
- Improves taste.
21. What Is a Mineral Cartridge?
A mineral cartridge re-adds calcium, magnesium, and other healthy minerals after RO purification.
22. What Is PSI?
PSI (Pounds per Square Inch) measures water pressure.
- RO systems typically need 40–100 PSI.
23. What Is Crossflow Filtration?
In RO, water flows across the membrane rather than straight through.
- Prevents clogging.
- Ensures continuous filtration.
24. What Is Salt Rejection?
Similar to rejection rate, salt rejection measures how well an RO membrane removes dissolved salts.
- Expressed as a percentage.
- A 98% salt rejection membrane allows only 2% of salts through.
How These Terms Work Together
When you combine these terms, you understand the entire flow of an RO purifier:
- Pre-filters (sediment & carbon) → protect the system.
- Booster pump → provides pressure.
- RO membrane → filters salts and microbes.
- Flow restrictor, check valve, and flush valve → manage water flow.
- Storage tank → holds permeate.
- Post-filter → improves taste.
- TDS controller or mineral cartridge → adds minerals back.
Why Learning RO Terms Helps You
- Better maintenance: You’ll know when to replace which part.
- Smarter buying decisions: You’ll understand which features you need.
- Cost savings: Avoid unnecessary service charges by knowing the basics.
- Health protection: Ensures you’re drinking safe water.
Conclusion
Understanding common RO terms isn’t about becoming a technician—it’s about taking control of your health and your home. From TDS and micron ratings to RO membranes and booster pumps, every term reflects a function that keeps your water clean and safe.
The next time you read your purifier’s manual or talk to a service technician, you won’t feel lost. You’ll be informed, confident, and able to make the best decisions for your family’s drinking water.
Hasan Al Sarker is a Reverse Osmosis Specialist. He has worked for many years to ensure safe drinking water for all. His research paper has been published in several journals, including Issue, Medium, and Slideshare. He is recognized as a water doctor among specialists though he did not attend medical college.
Besides working as a researcher of reverse osmosis technology, he is also very fancy with the kitchen and cooking. His guides are reading thousands of people every day. As a head of content, he is responsible for all the published articles at RO System Reviews.