How does reverse osmosis work?

How does reverse osmosis work?

Believe it or not, reverse osmosis (RO) really isn’t as complex as it sounds.

But before we leap into how it works, we just wanted to spend a minute briefly explaining what it is. Generally speaking, reverse osmosis is:

A technique that’s used to remove dissolved solids that are present in water by separating them using a process that’s derived from the naturally-occurring phenomenon, known as osmosis.

Reverse osmosis is mainly used to remove dissolved salts, particles, bacteria, molecules and minerals that are present in water. It’s commonly used by the pharmaceutical, manufacturing and metal finishing companies, as well as within food and beverage production, water jet cutting and glass, boiler and cooling tower pre-treatment processes.

And here’s a bit more of a technical explanation –

Reverse osmosis is when pressure is applied to a highly-concentrated solution that is usually high in salts. This pushes pure water through a semi-permeable membrane into a solution of low salt concentration. The pressure is needed to overcome the naturally-occurring osmotic pressure. The amount of pressure needed varies, depending on the ionic charge of particles and molecular weight.


Here’s a step-by-step overview of how reverse osmosis works…

  1. Water is forced under pressure through a membrane.
  2. Pure water pushes through the membrane.
  3. Small particles or impurities, such as bacteria, chemicals, salts and heavy metals, are left behind on the other side of the membrane.
  4. The reject water containing the contaminants goes down the drain or can be reused (keep reading for more on this).
Reverse Osmosis Systems

Reverse Osmosis System

Demin or RO?

Reverse osmosis has long been the subject of many a debate, mainly around the fact whether or not it’s more effective than its demin plant counterpart. One standout point about reverse osmosis is that it doesn’t require any resin or chemicals, such as acids or caustic. This means you don’t have to worry about being Control of Substances Hazardous to Health (COSHH) compliant too.

However, the truth of the matter is, both systems have come a long way in recent years and deciding which option to choose very much depends on which system is better suited to your requirements. For more insight on the demin v RO debate, check out this video with our Managing Director, Emma Armitage, in which she discusses the merits of both options.

Demin systems aside, the benefits of using reverse osmosis are widespread

  • They’re designed to run continuously – meaning there’s no downtime and the energy requirements are low
  • They can be built in different sizes and flow rates – from 300 litres an hour to 30,000 litres an hour
  • They can be designed to only reject 25% of the water – where possible we specifically design them this way, making them more water efficient than historical systems that reject 50% water
  • The reject water isn’t reject water – due to the fact it’s high in salts and minerals. It can be used elsewhere on-site for cleaning purposes which, in turn, means there’s less waste overall

The consequences of not using reverse osmosis are as diverse as the sectors that use it

For instance, within the glass industry, glass can become streaky and require more water to rinse it. In the personal care sector, products such as mouthwash can end up with particles in them, preventing them meeting the required standards. Meanwhile, a shampoo manufacturer may find using mains water to produce their products means contaminants are present that prevent them from working effectively.

Reverse osmosis is a water purification game-changer and the results it can produce are literally crystal clear. However, as with all water purification systems, there are all sorts of RO plants, as well as other options to choose from. Achieving the clearest water and the most efficient process involves investing in a system that’s tailored to your requirements.

Our Reverse Osmosis Systems

For more information about reverse osmosis or help and advice on selecting a system to purify your water (and help you produce your product(s) more efficiently and reduce downtime in the process) contact us on 0113 232 0005 or