Reverse Osmosis or Ultrafiltration, which one is the better technology for my home?
Reverse osmosis and ultrafiltration, commonly referred to as RO and UF, use membrane technology. The reverse osmosis system uses a semipermeable membrane that separates 99.99% of inorganic dissolved material from the water molecule.
The ultrafiltration system uses a hollow fibre membrane to stop solid debris and microscopic contaminants. UF is a mechanical filter, but it can filter water down to the superfine level of 0.025 micron, hence the name ultrafiltration. Ultrafiltration is a filter system, while reverse osmosis is a process where molecules are separated.
Water filtration technologies
Membranes remove unwanted components and ensure stable water quality. They consist of porous films, with defined pore diameters.
A membrane is a material that allows some substances to pass through and retains others – a selective barrier. A given membrane material retains components of a certain size or with certain chemical properties. In membrane filtration of water, pressure is used to get purified water through the membrane, while retaining unwanted components.
Water filtration membranes can be characterised by pore size. The pore size determines which components are retained (as shown in the figure below). The type of membrane filtration process is chosen based on wanted water quality.
What RO removes:
Reverse osmosis eliminates the majority of the dissolved minerals in the water. Many people prefer this because they want their drinking water as pure as possible, and entirely free from minerals, salts, and total dissolved solids (TDS). If you do want to preserve minerals in your RO water, you will have to add a remineralisation filter.
What UF removes:
Ultrafiltration is not going to eliminate dissolved solids or salts. Ultrafiltration only filters out solid particulate matter, but it does so on a microscopic level. Because it has such a fine micron reduction capacity, ultrafiltration will filter out the vast majority of contaminants like sediment, chlorine, and cysts.
| Reverse Osmosis | Ultrafiltration | |
| Arsenic | ✔ | X |
| Bacteria | ✔ | ✔ |
| Calcium | ✔ | X |
| Copper | ✔ | ✔ |
| Cysts | ✔ | ✔ |
| Fluoride | ✔ | X |
| Lead | ✔ | ✔ |
| Magnesium | ✔ | X |
| Nitrates | ✔ | X |
| Pharmaceuticals | ✔ | ✔ |
| Protozoa | ✔ | ✔ |
| Salts | ✔ | X |
| Sulfates | ✔ | X |
| TDS | ✔ | X |
| Viruses | ✔ | ✔ |
Storage and Conservation
RO membranes are without question the safest way for you to filter your water at home, but this performance comes with a price. The membrane function in a way that requires three things: A storage tank because of its low flow rate, an additional pump due to the minimum water pressure for it to function properly and a drain line caused by the cross flow nature of the technology which produces waste water for every liter of clean water purified.
UF technology doesn’t require a storage tank. It hooks directly up to the faucet due to its high flow rate. Both systems require a dedicated faucet, they won’t run straight to your kitchen sink faucet unless you have a 3-way tap installed, which combines hot, could and filtered water lines.
Installation
RO water filtration systems are quite complex and can be rather difficult to install. Beside the water input there has to be a drain line hooked up and the necessary storage tank has to be connected. All these components and connections carry the possibility of failure, so if you want to have peace of mind you should get it installed by a professional.
UF systems have a more simple general setup and requiere therefore less steps during installation. Less steps means less possible confusion. None the less it is a major intervention into your home water supply and should be carried out by someone with the right qualification.
Cost
RO membranes in average cost around 50% more than the usual ultrafiltration device but can last up to 3 times the lifespan. So when it comes to maintenance you will surly save money in the long run.
UF devices have an average lifespan for about a year depending on the source water they filter and how much water is filtered in total. The water filtration system with which both options, RO and UF are advertised and normally installed differ in overall costs as well. Because RO Systems often come with a more advanced technical setup like booster pump and storage tank they can cost you up to 2 times the price.
Conclusion
If you are looking for water with the highest degree of purity, RO is the technology to go for. There are system solutions on the market available which optimise the reverse osmosis process and run clean water production with best efficiency. Check out the Osmo from Osmosys for example. With a booster pump and internal anti-back-pressure tank the intelligent reverse osmosis membrane purifies water with a minimum amount of waste water.