A micron is a unit of measurement used to describe particle size. In water filtration, a micron rating tells you the approximate size of particles a filter is designed to capture.
Given that, it’s easy to assume that the smaller the number, the better the filter. But here’s the key: Micron ratings don’t tell you everything about water quality, filtration capabilities — or which filtration system is right for your home.
In this guide, we’ll break down:
- What a micron is and why it matters
- How micron ratings work in real-world filtration
- How to choose the right approach based on your water
- Where micron filtration fits into a complete water solution
What is a micron in water filtration?
A micron (or micrometer) is one-millionth of a meter. To put that into perspective, the smallest particles visible to the human eye are roughly 40–100 microns in size.
In water filtration, micron size refers to the approximate size of particles a filter is designed to reove. Depending on the filter design, this may involve surface pores or a layered filter media that traps particles throughout its structure.
Common particle sizes in drinking water
Understanding particle size helps put micron ratings into context.
- ~100–1,000 microns: Larger particles like sand, grit and visible debris
- ~20–180 microns: About the width of a human hair
- ~4–12 microns: Parasites such as Cryptosporidium (4–6 microns) and Giardia (8–12 microns)
- ~1–10 microns: Fine sediment and some larger microorganisms (note that most bacteria are smaller and require specialized filtration)
- <1 micron: Very fine particles (note that certain absolute-rated filters (read more about these later) – typically around 0.2 microns – can reduce bacteria, but most residential filters are not designed to provide full microbiological protection)
It’s also important to note that micron ratings only focus on blocking physical particles. Many dissolved contaminants, such as heavy metals or certain chemicals, require additional treatment beyond just decreasing pore size.
How micron ratings work (and what they actually tell you)
In simple terms, a higher micron rating is used for larger particles, while a lower micron rating is used for smaller particles. So, if you’re comparing a 50-micron filter to a 5-micron filter, the 5-micron option is designed to capture finer sediment and debris.
Typical micron ranges for home water treatment
Different micron ranges serve different purposes in a filtration system. These filters are typically used for sediment reduction, meaning they target physical particles rather than dissolved contaminants.
- 50–100 microns: Coarse filtration for larger particles like sand and rust
- 10–20 microns: General sediment reduction
- 5 microns and below: Fine particles that affect clarity and performance
- Sub-micron filtration (<1 micron): Very fine particles, typically used alongside advanced systems
Most homes don’t rely on a single micron filter. Instead, effective systems use multiple stages, moving from coarse filtration to finer filtration.
This layered approach helps:
- Capture larger particles first
- Improve overall filtration efficiency
- Reduce clogging and help maintain water pressure at fixtures
- Extend the life of each filter cartridge
That sounds straightforward, but micron ratings only tell you part of the story.
Nominal vs. absolute micron ratings
In most residential applications, micron filters are considered nominal filters. That means they can reduce a high percentage of particles at a given size, but not necessarily all of them. As Gary Falkengren, Culligan’s problem water specialist, explains, “A typical cartridge filter rated for 5 microns may capture about 80% of particles in that range, while some may still pass through.”
There are also absolute filters, which are built to block nearly all particles at a specific size. These are more common in high-purity environments like laboratories, pharmaceutical applications or food processing, but some residential drinking water systems also use absolute-rated filtration for specific applications.
What micron ratings don’t tell you
Micron ratings describe how a filter handles physical particles like sediment, rust or suspended solids. But they don’t tell you whether a system can address most dissolved substances like salts, metals or other water quality concerns.
That’s why micron ratings are helpful, but they’re not a complete measure of filter performance. They can tell you what size particles a filter is built to reduce, but they can’t tell you everything about how that filter will perform in your home or whether it’s the right solution for your water.
How to choose the right filter for your home
For the best match, you’ll want to choose a water filter that addresses your specific water quality concerns and goals. Culligan offers a free water test and consultation to help you identify what’s in your water and how best to address it.
That said, here’s where you can start your own research:
1. Start by understanding your water source and water quality.
Your water source plays a big role in the type and size of particles you may encounter:
- Municipal water: Typically treated, but may still contain sediment from pipes or distribution systems
- Well water: Often has higher levels of sediment, debris and suspended solids
Because these conditions vary, the most effective first step is a professional water test. This helps identify:
- The presence of sediment or particulate matter
- Whether particles are large, fine or dissolved
- Which filtration technologies are most appropriate
Worried about your well water?
2. Match filtration options to your goals.
Different filtration goals call for different approaches:
- Reducing visible sediment and debris: Use coarse filtration followed by finer micron filters
- Improving taste and odor: Combine micron filtration with carbon filters or activated carbon
- Protecting plumbing and appliances: Use sediment filtration as a first line of defense to capture larger particles (water softening would typically be recommended here as well, depending on water test results)
- Providing cleaner drinking water: Pair fine micron filtration with technologies like reverse osmosis, designed to address water concerns that may affect the safety, taste, appearance and overall quality of the water you drink.
Implement additional treatment if needed.
Micron filtration works best as part of a broader water filtration system. Some concerns require additional technologies:
- Dissolved minerals (hardness): Water softeners
- Chemical contaminants: Carbon filters or granular activated carbon, as well as reverse osmosis
- More advanced filtration: Reverse osmosis
For example, reverse osmosis systems often include:
- A sediment pre-filter (typically around 5 microns)
- Carbon filters for chemical reduction
- A semi-permeable membrane that filters dissolved contaminants at the molecular level, far smaller than what micron-rated filters can capture
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Filtering out the misinformation around micron filtration ratings
There are several common misconceptions about micron filtration ratings. Clearing these up can help you make more informed decisions.
Myth: The lower the micron rating, the better the filter.
This is not always true. Ultra-fine filters can clog more quickly, especially in water with high sediment levels. This can lead to reduced flow, increased maintenance and higher pressure drop.
The best micron rating depends on your water, not just the smallest pore size available.
Myth: Micron ratings tell you everything about what a filter removes.
They don’t. Micron ratings describe particle size, not specific contaminants. For example:
- Chlorine is reduced by activated carbon, not pore size.
- Dissolved minerals require ion exchange or reverse osmosis.
- Some harmful contaminants are too small for standard micron filters.
Micron filtration is primarily a form of sediment filtration—it removes physical particles, not dissolved or chemical contaminants.
Myth: A sub-micron filter makes water completely safe to drink.
Sub-micron filtration can capture very fine particles. Certain absolute-rated filters (typically around 0.2 microns) can reduce bacteria, but most residential filters are not designed to provide full microbiological protection.
Safe drinking water depends on:
- The type of contaminants present
- The filtration technologies used
- Verified performance through certification
For example, systems with NSF/ANSI Protocol P231 certification (like Culligan’s Aquasential® Smart Reverse Osmosis Drinking Water Filtration System) are tested for reduction of bacteria, viruses and cysts under controlled conditions. This type of certification goes beyond micron ratings by verifying microbiological purification performance—not just particle reduction.
Myth: All filters with the same micron rating perform the same way.
Filters with the same micron rating can vary significantly in:
- Filter media
- Design and construction
- Surface area
- Filtration efficiency
As noted above, most residential filters are nominal filters, meaning they capture a percentage of particles in a given size range, but not all of them. This is why checking capabilities as verified by testing and certification is so important (more on that below).
The limits of micron ratings: Why testing and certification still matter
Micron ratings are helpful, but they focus solely on particle size, which means you miss the full picture of water quality.
For example:
- They don’t indicate which contaminants are reduced.
- They don’t address dissolved substances like salts or heavy metals.
- They don’t guarantee safe drinking water on their own.
Certain water issues require entirely different approaches. That’s why testing and certification are essential. For example, for microbiological concerns, certifications like NSF/ANSI Protocol P231 evaluate a system’s ability to remove bacteria, viruses and cysts. This provides a higher level of assurance than micron ratings alone, which only describe particle size.
Overall, third-party certifications such as NSF/ANSI standards verify that a filtration system:
- Has been tested under controlled conditions
- Reduces specific contaminants
- Meets defined performance criteria
This is especially important when evaluating claims about bacteria reduction, chemical contaminants or overall filtration performance.
Micron filtration FAQs
Is a lower micron rating always better?
No. Lower micron ratings capture smaller particles, but they can clog faster and aren’t necessary for every home. The right choice depends on your water and filtration system design.
What does a 5-micron filter actually remove?
A 5-micron filter targets fine sediment such as silt, dirt and rust particles, and may reduce some larger microorganisms—but it does not remove bacteria or dissolved contaminants.
Do micron ratings tell me if a filter removes chemicals like chlorine or PFAS?
No. Micron ratings describe particle size, not chemical removal. Carbon filters and reverse osmosis systems with advanced filtration stages are typically used to address these types of contaminants.
What micron rating do I need for well water?
Well water often benefits from a staged approach, starting with coarse filtration for larger particles and moving to finer filtration as needed. A water test can help determine the right setup.
How do I know which micron filters my home needs?
The best way is to start with a professional water test. This identifies the size and type of particles, as well as other potential issues, impacting your water so you can choose the right combination of filtration technologies.
Avoid the guesswork with a professional water test
Micron filtration plays an important role in improving water clarity and helping protect your home, but it’s only one part of the solution.
The right filtration system depends on the size and type of particles in your water, whether dissolved contaminants are a concern and your household’s specific needs.
A local Culligan water expert can test your water, explain the results, recommend the right combination of filtration technologies and install and maintain a solution tailored to your home.
Start with a free water test so you can get a clearer picture of your water and choose the right solution with confidence.
