Reverse Osmosis vs. Ultrafiltration

Reverse osmosis and ultrafiltration are two of the most powerful and effective water filtration systems on the market. Though both RO and ultrafiltration possess remarkable filtration properties, the systems do have key differences. From mineral retention to ease of installation and cost of maintenance, each system has unique advantages and disadvantages. 

John Woodard, our Master Water Specialist, breaks down the differences between reverse osmosis and ultrafiltration. A better understanding of the two systems can help you decide which one is right for your home. 

UF vs. RO

Reverse osmosis and ultrafiltration, commonly referred to as RO and UF, use membrane technology. The reverse osmosis system uses a semipermeable membrane that separates 95-98% of inorganic dissolved material from the water molecule.

The ultrafiltration system uses a hollow fiber 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.

Minerals and TDS

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 are looking for water with the highest degree of purity, RO has the advantage. If you do want to preserve minerals in your RO water, you will have to add a post-filter remineralizer. 

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. For people who want to retain minerals like calcium and magnesium in their water, ultrafiltration has the advantage. 

Storage and Conservation

Reverse Osmosis is a cross flow filtration. The system creates two water streams through the membrane. One path ends up in a storage tank. Reverse osmosis makes water so slowly you have to store it to make it available. The tank takes up room under the counter. So, the RO storage tank could be a disadvantage for many people, as well as the slow filtration speed.  

A reverse osmosis system also has to hook up to the drain because the water carrying all of those dissolved inorganic materials away is going to be flushed out. For every gallon of water reverse osmosis purifies, about four gallons are converted to wastewater. This could be a disadvantage from a water conservation standpoint. To alleviate this, a permeate pump can be installed on an RO system to reduce the amount of wastewater and improve efficiency. 

Ultrafiltration doesn't require a storage tank. It literally hooks directly up to a special faucet. Both systems will require a dedicated faucet, they won't run straight to your kitchen sink. But the ultrafiltration system comes through the filter at a gallon per minute with no storage tank need. Ultrafiltration not produce wastewater, in fact, it can be used to make wastewater potable. It also operates even under low water pressure. RO cannot produce quality water under 50 psi, meaning you may have to install a water booster pump. This is a distinct advantage of ultrafiltration.

Installation 

RO installation:

A reverse osmosis system is more complex to install. More connections need to be made for the system to operate correctly. Water goes through an air gap faucet for backflow prevention. It hooks up to the drain line. It hooks up to the storage tank. Since it is filtering water through a complex process, it naturally requires more components. 

UF installation:

To install an ultrafiltration unit is very simple. You connect the feed supply and the other end of the filter. Then you connect directly to the dedicated faucet. So, for ease of installation, ultrafiltration systems have the advantage. 

Cost

How much does RO cost?

Residential reverse osmosis systems cost about $200-400. The initial cost of reverse osmosis is going to be a little higher than the cost of an ultrafiltration system. Reverse osmosis requires more components to buy and install, like a storage tank, a booster pump, a permeate pump, or a remineralizer. However, the RO membrane has a longer lifespan than the ultrafiltration membrane, and the system itself will require less replacement parts. 

How much does UF cost?

Ultrafiltration systems cost about $150-200 for the system itself. The ultrafiltration system is cheaper initially, but will cost more long term. You will have to replace the ultrafiltration system's filters and hollow fiber membrane more frequently than you'll need to replace the reverse osmosis membrane. So, while RO may be more expensive on the outset, the frequency of necessary replacements makes ultrafiltration the more expensive system to maintain.