Reverse osmosis (RO) is a common RO water treatment technology that uses water pressure and an RO membrane to separate out some of the dissolved substances and impurities in water. This article explains, in five steps, how an RO system works, its main components, and why pre-treatment and regular maintenance affect long-term performance.
How it works
An RO system uses water pressure to separate contaminants from the water. It works like this:
- Pre-treatment: Raw water first passes through pre-treatment, which removes larger material such as sediment, rust, chlorine and organic compounds and improves the water before the membrane. Pre-treatment usually includes a sediment (PP cotton) filter and activated carbon filtration.
- High-pressure pump: Pre-treated water enters a high-pressure pump, which applies pressure (typically about 60–80 psi) to push the water through the RO membrane.
- RO membrane: The RO membrane's pores are extremely small (about 10 Å), blocking the great majority of contaminants such as metal ions, viruses, bacteria and organic matter. Under pressure, water molecules pass through the membrane to the other side as product water, while contaminants stay on the feed side.
- Post-filtration: finally, the water passes through a post activated-carbon filter, which further removes any remaining odours and impurities to refine the water.
- Product water and concentrate (waste water): Water that passes the membrane and post-treatment is used as product water; the concentrated stream that does not pass is called concentrate, or waste water — it carries away part of the separated material and is discharged by the system.
Characteristics of the RO membrane
- Membrane materials: Membranes are usually cellulose ester or polyamide types, in spiral-wound, hollow-fibre or tubular structures.
- Rejection rate: RO membranes reject up to 90–98% of monovalent ions and up to 95–99% of divalent ions, and also effectively block substances with a molecular weight above 300.
- Maintenance needs: With use, a membrane's selectivity and flux gradually decline, so it needs periodic replacement to keep the system running reliably over the long term.
An RO system is more than the membrane itself — the pre-filters, high-pressure pump, post-filters and regular maintenance all count. Sensible pre-treatment reduces the load impurities place on the membrane, while replacing filters on schedule and checking the system's condition helps sustain long-term performance. When choosing an RO water filter, weigh the feed water conditions, installation environment, daily usage and maintenance arrangements together.
To choose a household Water Purifier or RO water dispenser, pick an option that fits your household's water habits, installation space and maintenance needs. Bio-Link's current home recommendations include:
- RO838: for households that want an under-sink RO filter in the kitchen, covering daily cooking and drinking needs.
- DT400: for households or small spaces that need a countertop hot-and-cold machine, with optional filtration as required.
For offices, schools, clinics or commercial premises needing a Office Water Dispenser, choose a model by daily headcount, installation position and maintenance arrangements. Bio-Link's current commercial recommendations include:
- ST1523: for offices or co-working spaces with higher water usage.
- ST9102: for schools, educational institutions or commercial premises with steady foot traffic.
- STC15: for offices, pantries or small-to-medium commercial premises where space is at a premium.
For businesses that value operational stability, the right drinking equipment and a regular maintenance schedule help reduce the impact of unexpected equipment problems on daily work; cutting bottled water and delivery trips also fits everyday environmental and ESG management.
Why choose Bio-Link?
Bio-Link was founded in Hong Kong in 1997, providing consultation, installation and maintenance for water filtration systems and hot-and-cold dispensers, serving homes, offices, F&B operators, hotels, educational institutions, community centres, medical organisations, research facilities and laboratories across Hong Kong and Macau. The team helps customers choose the right water filter and dispenser for their site needs, water-quality goals and maintenance arrangements.
Further reading on RO water
To first understand what RO water is, how reverse osmosis filtration works, and how to choose an RO filter for home, office, school or commercial use, read What is RO water.