Ultrafiltration vs Reverse Osmosis: The 2021 Definitive Comparison

Ultrafiltration vs Reverse Osmosis

For anyone whose drinking water is particularly high in contaminants, water filtration systems that can remove the highest quantity of impurities definitely have the biggest appeal.

One of the most popular, effective purification solutions is reverse osmosis. But there are other systems that are capable of removing a broad range of impurities, too, and ultrafiltration is one of them.

If you’re keen to learn about all your options before you decide which (if any) is for you, this guide should help you out. I’ll be comparing ultrafiltration and reverse osmosis, discussing their differences, their pros and cons, and ultimately sharing which process is, in my opinion, the best overall.

🤔 Is Ultrafiltration the Same as Reverse Osmosis?

While reverse osmosis & ultrafiltration are very similar, they’re not quite the same thing. I’ve explained how each process works below.

What is Ultrafiltration (UF)?

Ultrafiltration is a type of membrane filtration that uses a hollow-fiber membrane. Water is forced through this membrane, which typically has a pore size of 0.002 to 0.1 microns, depending on the system you opt for.

This water filtration process is usually installed beneath your kitchen sink, offering instant access to clean water via a dedicated faucet. It’s capable of removing bacteria, some viruses, suspended organic matter and a small amount of minerals.

What is Reverse Osmosis (RO)?

Reverse osmosis is another type of membrane filtration. It combines several stages of filtration, including a semi-permeable membrane, to remove more than 99.9% of total dissolved solids (TDS) from water.

A reverse osmosis system may be installed beneath your kitchen sink or on your countertop as a standalone water filtration unit. The pore size of a typical reverse osmosis membrane is around 0.0001 microns.

ContaminantReverse OsmosisUltrafiltration
Arsenic✔️
Bacteria✔️✔️
Calcium✔️
Chlorine✔️✔️
Copper✔️✔️
Cysts✔️✔️
Fluoride✔️
Lead✔️✔️
Magnesium✔️
Nitrates✔️
PFAS✔️✔️
Pharmaceuticals✔️✔️
Protozoa✔️✔️
Salts✔️
Sulfates✔️
TDS✔️
TTHMs✔️✔️
Viruses✔️✔️

💁 What’s the Difference Between Ultrafiltration and Reverse Osmosis?

To help you understand exactly what sets these two water filtration methods apart, I’ve broken down the differences between reverse osmosis & ultrafiltration below.

Semi Permeable Membrane Technology

While both reverse osmosis and ultrafiltration use membrane technology, the types of membranes used in each system are different.

An ultrafiltration system uses a hollow fiber membrane, usually with a slightly bigger pore size, which can remove microscopic pathogens and suspended particles.

A reverse osmosis system, on the other hand, uses a semipermeable membrane that has a much smaller pore size, blocking the majority of total dissolved solids and allowing only the smallest water particles to pass through.

filtration spectrum

TDS & Mineral Reduction/ Removal

The membrane used in a typical ultrafiltration system is designed to remove solid particles and organic compounds.

The benefit of ultrafiltration systems is that they can provide filtration at a microscopic level, making them capable of removing the notoriously difficult-to-remove contaminants, like bacteria, which are often small enough to squeeze through most water filters.

Keep in mind, however, that ultra-filtration can’t remove low-molecular weight dissolved particulate matter, like salts and dissolved minerals. If you’re looking to drink water that’s free from minerals, this method of water purification might not be for you. However, you may think that retaining water’s dissolved minerals is a plus point, especially as many of these minerals can help to support a healthy diet.

RO membranes are capable of eliminating the majority of total dissolved solids (TDS) from drinking water – and that includes solid and dissolved particulates.

If you’re looking to achieve pure water, RO systems are the best for the job. Like ultrafiltration, this method of water treatment can remove everything from lead and chlorine down to bacteria and viruses – but it also removes dissolved salts and minerals from drinking water.

Quick note: there are many methods of remineralizing, meaning you can still benefit from the highest quality pure water but with healthy minerals added back in. Find my guide on remineralizing reverse osmosis water here.

Additional Filtration Stages

Ultrafiltration is a filtration system in itself, and can be purchased as a standalone unit. You can choose to add additional stages of filtration before or after a UF mechanical filter if you want to reduce a broader range of contaminants, but generally, the system is purchased alone.

Reverse osmosis water filtration systems typically combine a semi-permeable membrane with a variety of additional filters for the highest quality of water treatment. It’s common for an RO filter system to include a sediment pre-filter, an activated carbon filter, and a post-filter alongside the RO membrane.

Wastewater

Comparing ultrafiltration vs reverse osmosis, reverse osmosis comes off a lot worse when looking at water waste. An RO filtration system produces constant water waste while in operation. This is because the contaminants that build up inside the RO chamber need to be flushed away, and doing so flushes away a batch of water in the process.

The promising thing about reverse osmosis filtration is that this water treatment system is becoming far more efficient.

While the traditional pure water to wastewater ratio is 1:4, nowadays, there are reverse osmosis filters that are capable of only wasting 1 gallon of water for every 1 gallon produced, so it’s far less wasteful. Of course, you’ll still be wasting water, but it shouldn’t be enough to contribute significantly to your water bill.

Ultrafiltration, on the other hand, wastes no water whatsoever. This is a huge benefit if you’re looking for the most cost-effective water filtration solution. I discuss cost in more detail in a later point.

Water Storage vs On Demand

Traditional cross-flow RO drinking water systems have a storage tank, where filtered RO water is kept before it makes its way to your faucet.

Reverse osmosis can be quite a slow water purification process, so the advantage of having a storage tank is that when you switch on your faucet, you can still get instant access to clean water. In the meantime, the system will refill the storage tank with the water that was lost, giving you a constant supply at all times.

An obvious disadvantage here is that a water storage tank will take up more space, which isn’t ideal if you don’t have a lot of room under your kitchen counter as it is. However, there are some RO systems available nowadays that don’t come with a storage tank. Their clever designs ensure that flow rate is always high enough to provide immediate access to RO water.

Ultrafiltration doesn’t need a tank for storing water. Like the majority of whole-house and under-sink filters, this water filter simply hooks onto your cold water line. When you turn on your faucet, water flows straight through the filter, back into the water line, and out of the faucet. This system shouldn’t affect water pressure – usually, water can pass through the membrane at a rate of 1 gallon per minute.

Installation

In terms of installation, reverse osmosis and ultrafiltration systems are fairly similar.

However, because reverse osmosis systems are more complex in design, they naturally take a bit more effort to install. You’ll usually need to make more connections from the unit to your water line, as well as hooking the system up to a drain line for the wastewater.

If you purchase a reverse osmosis system with a storage tank, that’s another part of the system that will need to be integrated into your under-counter space.

Ultrafiltration systems have fewer parts to worry about, which makes installation a much quicker process. Usually, you’ll just need to attach the filter to the cold water line, then connect the other end of the filter directly to the dedicated faucet.

There’s no storage tank or drain line to worry about, so this is a job you’re likely to be able to do yourself without the need for a plumber.

Dedicated Faucet

The majority of RO filters and ultrafiltration systems have their own dedicated faucet. The reason for this is that some kitchen faucets contain metals that may leach into your water after it has been filtered.

High-purity water is more susceptible to toxic metal leaching, so if water quality is important to you, you should make sure to install a dedicated faucet if it comes with your system. Many reverse osmosis and ultrafiltration units aren’t designed to connect to a standard tap, too, so in many cases, installing the dedicated faucet will be mandatory.

Cost

The upfront cost of a reverse osmosis system is roughly double the cost of a water ultrafiltration unit. While RO treatment filters usually cost around $300-$600, an entire ultrafiltration unit typically costs between $150 and $200.

You’ll also have to factor in the cost of filter changes for a reverse osmosis system, which will ensure that the system can continue to function properly. The carbon filter and pre- and post-filters typically last between 6 months and 1 year, while the RO membrane requires changing once every 2 years.

Ultrafiltration treatment also requires filter replacements. The hollow fiber membrane doesn’t last as long as a reverse osmosis membrane, so you’ll have to spend money more frequently on ensuring the system can continue to remove particles to a high standard.

🎭 Pros & Cons of UF vs RO

Advantages of a Reverse Osmosis System

Removes the most contaminants

One of the biggest benefits of this system is that RO removes an incredibly diverse range of contaminants, including dissolved minerals, lead, bacteria, calcium, magnesium, viruses, chlorine, metal ions, and VOCs. This high-quality contaminant removal is ideal for anyone who’s looking to benefit from the highest purity drinking water possible.

Makes water safe to drink

If your drinking water contains pathogens, you’ll want to know that the treatment method you use effectively removes these harmful impurities. Thanks to its tiny micron size, RO can remove pathogens as small as viruses, which most filters are unable to do.

Long-term savings

Reverse osmosis units might be costlier upfront, but they’re cheap to operate and can help you to save money over the years. The carbon filter, pre- and post-filters, and semipermeable membrane have longer lifespans than UF membranes, and you’ll no longer have to spend money on bottled water, which is one of this system’s biggest benefits.

Disadvantages with RO

Can’t operate with a low water pressure

A reverse osmosis unit requires a water pressure of at least 50 PSI to operate. Failing this, you might find that there isn’t enough force to send drinking water through the system. You can purchase a pressure pump to boost your water’s pressure, but this would come at an extra cost.

Water could taste flat

Because reverse osmosis removes calcium and magnesium from water, as well as monovalent ions like sodium, it might affect its taste. Minerals give water a pleasant alkaline taste, and without it, you might find that your water tastes flat. The only way to remedy this would be to use a remineralization filter.

Produces wastewater

Whether you’re using a whole-house RO unit or a more popular under-sink or countertop system, there’s no getting around the fact that reverse osmosis wastes water. From an environmental perspective, this isn’t great news. The wastewater will also contribute to your water bill.

Advantages of an Ultrafiltration System

Retains healthy minerals

Ultrafiltration doesn’t filter out mineral particles like calcium and magnesium. These particles in your water offer a number of health and taste benefits when compared to RO.

Removes microscopic contaminants

Because of the tiny micron pore size of an ultrafiltration membrane, the system can thoroughly eliminate particulate matter of all sizes, from lead and chlorine to bacteria and protozoa.

Can operate with low pressure

An ultrafiltration membrane doesn’t need a high water flow or pressure to operate. You wouldn’t need to buy a separate pressure pump to make sure this system could operate at its best.

Disadvantages of UF

Doesn’t get rid of all viruses

While a UF membrane has a very small micron size that can filter out bacteria, it may struggle to filter water that’s contaminated with viruses. This might not be ideal for you if you’re looking to filter drinking water that contains pathogens.

Can’t filter out dissolved ions

UF processes can’t remove natural dissolved molecules, such as minerals and salts. This system wouldn’t be able to treat hard water, which may be a disadvantage if you’re looking for a whole-house application that can remove magnesium and calcium.

NU Aqua Platinum Series review
NU Aqua RO system
waterdrop uf filter
Waterdrop UF system

🏆 So, Which is Better Reverse Osmosis or Ultrafiltration?

Both processes have their pros and their cons. I would suggest thinking about what you hope to achieve from a water filtration solution when you’re deciding between reverse osmosis and UF water filtration.

If you just want to remove solid molecules from water, while retaining healthy mineral ions, ultrafiltration is a fantastic option. However, many people prefer the thoroughness of RO filtration, with the added benefits of the extra carbon filter. No choice is right or wrong – it just depends on what you’re looking for.