Reverse Osmosis: Not the silver bullet it's made out to be

If you work in food production, good water quality is of high importance. For QA managers, it forms the basis of reliable and consistent process water. When managing this, the term reverse osmosis inevitably comes up. The technology often seems like a complete solution: it filters contaminants, nitrates and bacteria in a single step. But is it really?

What is RO and how does it work? 

In reverse osmosis (RO), water is forced through a semi-permeable membrane under high pressure. The pores of this membrane are extremely fine. The result: dissolved salts, heavy metals, nitrates, pesticides, pharmaceutical residues, bacteria, fungi and yeast present at the time of filtration are held back. What passes through the membrane is chemically almost pure water.

In industry, it is used for:

• Food and beverage: ingredient water, bottled water, CIP, boiler and cooling tower feed
• Electronics/semiconductor: high-purity rinse and process water
• Power and general industry: boiler feedwater, cooling tower make‑up, process water and water reuse.

What RO does well 

There are clear strengths of RO technology 

• Removes up to 99% of dissolved contaminants such as nitrate, heavy metals, PFAS, and scale-forming minerals (1).
• Noticeably improves the taste and chemical quality of water (2).
• Reduces carbonates that cause limescale in pipes. (1)(3).

For heavily contaminated source water in areas with high nitrate or iron levels, for example. RO can be a good solution. However, even perfectly filtered RO water can quickly become microbiologically unsafe once it leaves the membrane since RO does not remove bacteria fully making the water behind it is chemically pure, but not microbially. (4)(7)

What RO does not do 

RO removes bacteria at the membrane, at the moment of filtration. What it does not do is prevent bacterial regrowth in the pipes between the membrane and the point of use. And that is precisely where the real danger lies.

Industrial facilities measure water quality after RO and at the point of use. By measuring at these two points you know what happens within the waterpipes: the development of biofilm.

Biofilm and its recontamination risk 

In tanks and pipes, this unprotected water quickly becomes an ideal breeding ground for bacteria. This means:​

• Coliform bacteria, E. coli, Enterococci, and Pseudomonas aeruginosa have been found in RO-treated water downstream of the membrane​.
• Biofilm forms in downstream pipework  regardless of how clean the water was at the membrane.
• A poorly maintained RO system can itself become a source of contamination​.

Business cases: RO is not enough on its own (H3)

In practice, we’ve seen that even well‑maintained RO systems do not fully prevent microbiological growth in water lines and storage tanks. Several of our clients have experienced recurring bacterial contamination and biofilm formation downstream of their RO units, despite regular maintenance and filter replacement.
This shows why RO alone is not enough and why continuous disinfection is needed.

The Watter-System: HOCl Produced On-Site 

The Watter System  produces HOCl directly from water, salt, and electricity, using electrochemical activation (ECA). This means:​

• No delivery or storage of hazardous chemicals.
• Continuous disinfection throughout the entire pipe network to the drinking trough.
• Proven efficacy against viruses, bacteria, yeasts and fungi.
• Registered on the European Article 95 list for biocidal products (PT1–5)​.
• Independence from external suppliers, with no risk of over- or underdosing​.

Filtration + Disinfection: an effective strategy 

RO and active disinfection with HOCl are not alternatives; they are two systems that together form a complete water quality strategy. The table below compares reverse osmosis (RO) filtration with the Watter-System.

The most effective strategy for cleaner water is therefore: 

• RO: If your source water is chemically contaminated, then RO is the right first step. However, if your water is already chemically clean, a Watter system alone is sufficient to keep it microbiologically safe.
• Watter-System: as a continuous disinfection stage throughout the entire distribution network to also make the water microbiologically clean and help reduce the build of biofilm.

Together, RO and the Watter-System deliver water that is both chemically and microbiologically clean.

References:

1. Schoeman, J.J., & Steyn, A. (2003). Nitrate removal with reverse osmosis in a rural area in South Africa. Desalination, 155(1–3), 15–26. https://doi.org/10.1016/S0011-9164(03)00235-2
2. Vingerhoeds, M.H., de Vries, M.J., Hooglander, P.A., & van der Linden, E. (2016). Sensory quality of drinking water produced by reverse osmosis membrane filtration followed by remineralisation. Water Research, 94, 42–52. https://doi.org/10.1016/j.watres.2016.02.019
3. Kapepula, L.M., & Luis, P. (2024). Removal of heavy metals from wastewater using reverse osmosis. Frontiers in Chemical Engineering, 2, 1334816. https://doi.org/10.3389/fceng.2024.1334816
4. Park, S., & Hu, J. Y. (2010). Assessment of the extent of bacterial growth in reverse osmosis system for improving drinking water quality. Journal of Environmental Science and Health, Part A, 45(8), 968–977. https://doi.org/10.1080/10934521003772386
5. Choi, Y.-J., Lee, S., Koo, J., & Kim, S.-H. (2016). Evaluation of economic feasibility of reverse osmosis and membrane distillation hybrid system for desalination. Desalination and Water Treatment, 57(51), 24662–24673. https://doi.org/10.1080/19443994.2016.1152648
6. https://www.watter.nl/watter-systeem/
7. Park, S., & Hu, J. Y. (2010). Assessment of the extent of bacterial growth in reverse osmosis system for improving drinking water quality. Journal of Environmental Science and Health, Part A, 45(8), 968–977. https://doi.org/10.1080/10934521003772386