What Is Ultrafiltration? – A Complete Guide

Ultrafiltration systems are one of the more popular methods for water filtration. It’s often compared to and contrasted with reverse osmosis which is another popular choice. Ultrafiltration (UF) has a lot of pros and cons compared to reverse osmosis (RO) and to unfiltered tap water.

Here’s a breakdown of ultrafiltration and whether it’s right for your home.

How does ultrafiltration work?

How ultrafiltration works

Ultrafiltration is a system of hollow fiber membrane filtration that removes suspended solids, viruses, bacteria, endotoxins, and other pathogens from your tap water. It works on a simple principle – the pressure of the water itself pushes it through a series of semi-permeable membranes to filter out unwanted particles.

An ultrafiltration process first screens sand and other large particles of 10 microns or more. Next, it screens particles up to ~0.1 microns, which filters out most bacteria. Lastly, it filters viruses and other organic macro-molecules that are just 0.02 microns large.

All these filtration layers are a part of the same membrane, and the filtration happens instantaneously. The standard pore size of an ultrafiltration membrane is 103 to 106 Daltons (molecular weight of proteins).

In essence, ultrafiltration is one comprehensive semi-permeable membrane that filters solid particles from your water.

UF manufacturers classify their UF products based on their molecular weight cutoff (MWC). A UF with 100,000 MWC means that if you feed the UF system with water containing 100,000 daltons, the UF unit will filter (almost) all of them out. In other words, the MWC is the “capacity” of the UF unit.

What does ultrafiltration remove?

Ultrafiltration membranes remove most of the harmful pathogens that are commonly found in tap water. These include:

  • Proteins
  • Endotoxins
  • Plastics
  • Sediment
  • Pathogens like viruses, bacteria and spores

What ultrafiltration doesn’t remove

There are two key groups that UF systems leave in the water – salts and dissolved organics. This most commonly means that a UF system won’t remove the calcium and magnesium minerals that are often present in tap water. As both calcium and magnesium aren’t harmful but are even beneficial for people, that’s hardly a disadvantage.

There are some other minerals that also won’t be filtered by UF, however. These include:

  • Arsenic
  • Fluoride
  • Nitrates
  • Sulfates
  • TDS – total dissolved solids
  • Other salts

This is why it’s best to combine ultrafiltration with other purification methods to ensure a more comprehensive treatment of your water. No single water filtration method can remove 100% of the contaminants in the water. As a result, experts recommend combining different purification systems.  

Ultrafiltration vs. Reverse Osmosis

The quickest way to explain the difference between ultrafiltration and reverse osmosis is that:

  • UF is a mechanical filter membrane that simply stops physical particles of certain sizes from passing through.
  • RO is a filtration process where particles are separated at a molecular level and the water is divided into two streams – clean water and waste water.
Reverse osmosis filtration process explained

This difference means several things:

  1. RO systems are much larger, more expensive, and complex to install than UF systems.
  2. RO systems throw away ~20-25% of your water as wastewater, leaving only the other 75-80% for drinking. This excess water is thrown away and can have a significant impact on your water bill.
  3. RO systems take a while to filter your water so they come with their own water tank where you can store pre-filtered water. UF systems, on the other hand, will filter your tap water almost instantly (about one gallon of water per minute), meaning no wait time.
  4. RO systems require a minimum water pressure of 50 psi (pressure per square inch) to work, making them unsuitable for homes with too low water pressure.
  5. RO systems clean your water completely, including removing all minerals that a UF unit will leave in. However, some contaminants, like solvents and VOCs, can get through an RO system.  

With those key points in mind, the pros and cons of UF and RO systems can be summed up like this:

ProsFilters water quickly at ~1 gallon per minuteProduces no wastewaterWorks well even at lower water pressure levelsFilters all types of solids, bacteria, viruses, endotoxins, and other pathogensIncludes no chemicalsSimple installation and automationEnvironmentally friendlyAffordable pricesLeaves in minerals such as magnesium and calciumHas a compact design that doesn’t take too much spaceFilters even more particles, including minerals, salts, and dissolved organicsProduces completely pure water
ConsDoesn’t filter everything, leaves in certain minerals, salt, and dissolved organics  Produces ~20% wastewaterRO filtration process takes more timeRequires a storage tank for the filtered water because of the slow filtration speedNeed a minimum water pressure of at least 50 psi to workInstallation is more complicated and time-consumingNeeds extra space near the sinkThe RO system is more costly to both purchase and run

Simply counting the number of pros and cons of UF and RO systems can leave the impression that UF systems are significantly better. The truth, however, is that both serve their purpose and have their place. Depending on what you have in your water supply and exactly what you want in your drinking water, either UF or RO can be better for your particular needs.

How to know what’s in your tap water?

Ultimately, the choice of whether you should get an ultrafiltration system, a reverse osmosis system, another filtration method, or nothing at all, falls to both personal preferences and what’s in your water supply.

If you want to test your tap water to see what’s in it, in what quantities, and what needs to be filtered out, there are a few things you can do:

  1. Most people who are on municipal tap water and pay their bills should receive an annual water quality report called Consumer Confidence Report (CCR). If you haven’t received yours, contact your local water supplier. If you rent – call your landlord. Additionally, municipal systems with more than 100,000 households also post their reports online here.
    In your CCR you’ll find a summary of what contaminants, if any, were found above governmental cutoffs in your municipal water supply. The report will also inform you of what the potential health risks are and what you can do to mitigate them.
  2. If you’re on well water, if you don’t trust the CCR, or if you suspect additional contaminants may be coming from your home’s plumbing, you can get your water tested. There are many DIY water test kits available but it’s advisable to use an EPA-approved lab to do this. You can check for the certification programs and certified laboratories for drinking water here. Testing usually costs between $20 and $150. Note that your community might be providing test kits free of charge.

Once you’ve determined what’s in your water, it’s up to you what you can do about it. There are many types of water filtration methods on the market, so choosing the right one for your home depends on your specific requirements.

The Bottom Line

Ultrafiltration is an excellent choice for treating water, as it removes most contaminants in your water. While it’s not a complete solution for purifying water, it offers many advantages which is why it has become a popular method for treating water.

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