Sediment Filter Micron Ratings Explained (1, 5, 10, 20, 50 Micron)
Sediment Filtration for Well Water
Sediment Filter Micron Ratings Explained (1, 5, 10, 20, 50 Micron)
A micron rating tells you the smallest particle a filter can catch. Lower number means finer filtration. But lower is not always better, because finer filters clog faster and reduce water pressure. After 30+ years of installing sediment filters for well water systems, I can tell you exactly which micron rating makes sense for your situation and why most homeowners are either over-filtering or under-filtering their water.
Want the full picture first? Start with our Complete Guide to Sediment Filters for Well Water. Or explore all of our sediment filter systems.
The Short Version
Micron ratings measure the size of particles a filter can capture. Here's what 30 years of field experience has taught me:
- For most well water homes: A 5 micron sediment filter is the standard recommendation. It catches fine silt, sediment, and particles without excessive pressure drop or constant cartridge changes.
- For heavy sand or grit: Start with a 50 micron spin-down filter before your pressure tank, then add a 5 micron Big Blue cartridge after it. This staged approach protects your equipment and catches everything.
- For cyst protection: A 1 micron absolute rated filter is required by NSF/ANSI Standard 53 to remove cryptosporidium and giardia.
- Nominal vs. absolute matters: A "nominal" 5 micron filter might only catch 85% of particles that size. An "absolute" 5 micron filter catches 99.9%. Always ask which rating you're getting.
- Need help choosing? Call Aidan at 800-460-5810 with your water test results and he'll recommend the right micron rating for your system.
What Micron Rating Do You Need?
Answer 3 quick questions for a recommendation
What's in your water?
Pick the best description of what you're seeing
Where in the plumbing line will this filter go?
This affects which type and micron rating is best
How many people live in your home?
Higher usage means you need to balance filtration with flow rate
50 Micron Spin-Down Filter
For visible sand and grit before the pressure tank, you want a Rusco spin-down sediment filter with a 50-60 micron screen. This catches the heavy stuff before it can damage your pressure tank and downstream equipment. No cartridges to replace; just open the flush valve periodically.
For the best protection, pair it with a 5 micron Big Blue cartridge filter after the pressure tank to catch the fine particles the spin-down misses. Call Aidan at 800-460-5810 to confirm this setup for your system.
5 Micron Cartridge Filter
For your situation, a 5 micron Big Blue sediment filter is the right choice. This is what we install on the vast majority of well water systems. It catches fine silt and sediment without causing pressure problems or needing constant cartridge changes.
The 20" Big Blue kit ($195) includes the housing, mounting bracket, wrench, and a 5 micron cartridge. Replacement cartridges run about $45 and typically last 3-6 months depending on your sediment load. Call Aidan at 800-460-5810 if you'd like help sizing your system.
1 Micron Absolute Filter + UV Disinfection
For protection against giardia and cryptosporidium, you need a 1 micron absolute rated filter. NSF/ANSI Standard 53 requires this rating for cyst reduction. However, a filter alone will not kill bacteria or viruses.
For complete microbiological protection, pair a 1 micron sediment filter with a UV disinfection system. The filter catches cysts and sediment; the UV kills bacteria and viruses. This combination is the gold standard for well water safety.
Call Aidan at 800-460-5810 to discuss your water test results and get the right setup.
What Is a Micron?
A micron (short for micrometer, abbreviated μm) is one-millionth of a meter, or one-thousandth of a millimeter. That's far too small to see with the naked eye. To put it in perspective:
When a sediment filter has a "5 micron" rating, it means the filter is designed to catch particles that are 5 microns (0.005 mm) and larger. Anything smaller than 5 microns passes through.
Particles you can see with your naked eye are at least 40 microns. That means a 5 micron filter catches particles roughly 8 times smaller than what you can see. This is why water can look perfectly clear but still contain fine sediment that damages treatment equipment, clogs fixtures, and shortens appliance lifespan.
Why This Matters for Well Water
Municipal water is pre-filtered before it reaches your home. Well water is not. It comes straight from the ground carrying whatever particles are in the aquifer and the well casing. Sand, silt, clay, rust from iron pipes, and even microscopic organisms all need to be removed, and the micron rating of your filter determines what gets caught and what gets through.
Micron Size Chart: What Each Rating Catches
This chart maps common well water contaminants to the micron rating needed to filter them. The bar width represents how fine the filtration is: shorter bars catch smaller particles.
Sediment Filters Do Not Remove Dissolved Contaminants
Micron filtration only catches physical particles suspended in water. Dissolved contaminants like iron in solution, hardness minerals, hydrogen sulfide (rotten egg smell), and chemicals pass right through any sediment filter regardless of micron rating. For dissolved contaminants, you need treatment-specific media: an iron filter for dissolved iron, a acid neutralizer for low pH, or a water softener for hardness. Sediment filters protect that equipment by catching particles first.
The Pressure Drop Tradeoff: Why Finer Is Not Always Better
This is the part most articles skip. Finer filtration sounds better, but there's a real cost: pressure drop. The finer the filter, the harder water has to push through the cartridge. This reduces flow rate and water pressure at your fixtures.
These are approximate values for a clean, new cartridge at typical household flow rates (5-10 GPM). As the filter loads with sediment, the pressure drop increases until you replace the cartridge. A 1 micron filter in a home with heavy sediment might only last a few weeks before the pressure drop becomes unacceptable.
This is exactly why we recommend 5 micron as the standard for most well water applications. It's the sweet spot: fine enough to protect your downstream equipment (iron filters, acid neutralizers, water softeners) and catch silt that would otherwise build up in treatment tanks, but coarse enough to maintain decent flow rates and cartridge life.
The Real-World Test
After installing thousands of sediment filter systems, I can tell you that 5 micron is what works for the overwhelming majority of well water homes. A homeowner in Massachusetts recently called asking why Home Depot only had 20 and 25 micron filters. Those "only take out really large particles," as I told him. The 5 micron cartridge in a 20" Big Blue housing is the setup we use on every installation, and it's what I'd put in my own home.
Why Staged Filtration Works Better Than a Single Filter
If you have significant sediment (visible sand, grit, or heavy turbidity), trying to catch everything with a single fine filter is a losing battle. The filter clogs fast, you're changing cartridges every few weeks, and the pressure drops between changes are frustrating.
The better approach: use two filters in sequence, each doing a different job.
Well Water Enters
Raw water from the well, carrying sand, silt, and sediment particles of all sizes
50μm Spin-Down
Catches large sand and grit. Flush valve to clean; no cartridges to replace. Installed before the pressure tank.
Pressure Tank
Sand-free water enters the tank. Tank bladder lasts longer. Pressure is maintained.
5μm Big Blue
Catches fine silt and particles that passed the spin-down. Protects iron filters, softeners, and UV systems downstream.
Clean Water
Sediment-free water flows to treatment systems and throughout the home.
The spin-down does the heavy lifting (catching the large particles that would clog a fine filter immediately), and the Big Blue cartridge polishes the water to catch the fine stuff. Each filter operates in its strength zone, and the cartridge in the Big Blue lasts much longer because it's not dealing with sand and grit.
This staged approach is the standard recommendation for any well water system. It's what we install on every system we set up, and it's what I recommend when customers call asking about filtration. A homeowner called recently asking about using 50 and 30 micron filters in front of his iron filter. Those sizes "filter out fairly large particles. They're not really doing a whole lot" for protecting equipment. The 50-to-5 combination is what actually works.
When to Use Each Micron Rating
Each micron rating has a specific use case. Here's when each one makes sense based on real installation experience.
Nominal vs. Absolute Ratings: What the Industry Doesn't Tell You
Not all micron ratings are created equal. There are two ways manufacturers rate their filters, and the difference is significant.
| Rating Type | Capture Rate | What It Means |
|---|---|---|
| Nominal | 60-90% of particles at rated size | A nominal 5 micron filter catches most particles that size, but some get through. Exact capture rate varies by manufacturer. It's a rough guideline, not a guarantee. |
| Absolute | 99.9% of particles at rated size | An absolute 5 micron filter catches virtually every particle 5 microns and larger. This is a tested, verified standard. Required for cyst reduction certifications. |
The practical difference: a nominal 5 micron filter might let 10-15% of 5 micron particles through. An absolute 5 micron filter lets through less than 0.1%. For general sediment protection, nominal is fine. For health-related filtration (cyst reduction), you need absolute.
Watch Out for Misleading Ratings
Some manufacturers label their filters with a range (like "25-1 micron") which is called a "nominal" or "graded density" rating. A customer recently called with a filter rated "one nominal" that the manufacturer described as "like a 25-to-1 micron." That's misleading. The outer layer catches 25 micron particles while the inner core catches down to 1 micron, but the overall capture rate at 1 micron is nowhere near 99.9%. If you need actual 1 micron protection, look for "1 micron absolute" on the packaging and an NSF/ANSI 53 certification for cyst reduction.
Most standard sediment cartridges (polyspun, string-wound, pleated) are nominal rated. This is perfectly acceptable for protecting treatment equipment and general sediment removal. The polyspun 5 micron cartridges in our Big Blue kits are nominal rated and do an excellent job for their intended purpose.
How to Know If You Chose the Wrong Micron Rating
The right micron rating should be something you rarely think about. You change the cartridge on schedule, water pressure is consistent, and downstream equipment stays clean. If that's not your experience, you may have the wrong rating.
⚠️ Signs Your Filter Is Too Fine
- Pressure drops noticeably within days or weeks of a cartridge change
- You're changing cartridges more than once a month
- Water pressure is significantly lower than it was before you installed the filter
- Multiple fixtures running simultaneously causes very low pressure
- The cartridge is completely packed with sediment when you remove it
Solution: Move up one or two micron sizes (e.g., from 1 to 5, or from 5 to 10). Or add a coarser pre-filter upstream to reduce the sediment load reaching the fine filter.
⚠️ Signs Your Filter Is Too Coarse
- Water still appears cloudy or hazy after filtering
- Fine sediment accumulates in toilet tanks and water heater
- Treatment equipment (iron filter, softener) fouls faster than expected
- A white or brown film collects on faucet aerators
- The cartridge looks relatively clean even after months of use
Solution: Step down to a finer micron rating. If you're at 20 or 25 micron, go to 5 micron. If you're already at 5 micron and still seeing issues, the problem may be dissolved contaminants (not particles) and you need a different type of treatment.
A quick test: pull the cartridge after a month of use. If it's solid brown/gray with sediment, the filter is doing its job. If it's still mostly white, you either have very clean water (unlikely with a well) or the micron rating is too coarse. If it's completely plugged and solid, the rating is too fine for your sediment load, or you need to add a pre-filter upstream.
Product Recommendations by Micron Rating
Here's what we carry for each common filtration stage. These are the same products we've been installing and recommending for decades.
| Product | Micron Rating | Best For | Price |
|---|---|---|---|
| Standard Rusco Spin-Down Filter | 50-100 μm (screen) | Pre-pressure tank, heavy sand, first-stage filtration | $145 |
| Large Rusco Spin-Down Filter | 50-100 μm (screen) | Higher flow rate homes, wells with heavy sand production | $165 |
| 10" Big Blue Sediment Filter Kit | 5 μm (polyspun) | Lower flow homes (1-2 bathrooms), compact spaces | $165 |
| 20" Big Blue Sediment Filter Kit | 5 μm (polyspun) | Standard recommendation for most homes, higher flow rate and longer cartridge life than the 10" | $195 |
| Pentek Replacement Cartridge (10" Big Blue) | 5 μm (polyspun) | Replacement cartridge for 10" Big Blue housing | $45 |
| Fleck 2510SXT Backwashing Sediment Filter | Multi-media (not cartridge-based) | Extremely heavy sediment where cartridge filters clog too fast | $1,895 |
For the majority of homeowners, the 20" Big Blue Sediment Filter Kit ($195) is the right choice. It comes with the housing, mounting bracket, wrench, and a 5 micron polyspun cartridge. The 20" housing provides better flow rates and longer cartridge life than the 10" version.
If you have heavy sand before the pressure tank, start with a Rusco spin-down ($145) and add the Big Blue after the tank. The spin-down catches the heavy stuff and can be flushed clean without a cartridge change. The Big Blue polishes the water after.
For wells with extremely high sediment loads where you'd be changing cartridges weekly, the Fleck 2510SXT backwashing sediment filter ($1,895) eliminates cartridges entirely. It uses a multi-media bed that backwashes automatically to flush out trapped sediment.
Not Sure Which Setup Is Right?
Send your water test results to Aidan at 800-460-5810. He'll look at your sediment levels, flow rate needs, and what other treatment equipment you have (or plan to add) to recommend the right micron rating and filter configuration. There's no charge for the consultation.
Frequently Asked Questions
Which is better: 5 micron or 20 micron for well water?
5 micron is better for well water in nearly all cases. A 20 micron filter lets fine silt and clay particles through, which build up inside treatment equipment and coat fixtures over time. The price difference between a 5 micron and 20 micron cartridge is minimal, so there's no cost reason to choose the coarser option. The only situation where 20 micron makes sense is if your sediment load is so heavy that a 5 micron filter clogs within days. In that case, add a 50 micron spin-down pre-filter first, then use the 5 micron.
Is a 1 micron filter better than a 5 micron filter?
It depends on what you're trying to accomplish. A 1 micron filter catches finer particles and can remove protozoan cysts like cryptosporidium and giardia (when absolute rated). But it also creates significantly more pressure drop and clogs much faster. For general sediment protection on well water, 5 micron is the better practical choice. For specific health concerns about cysts, use a 1 micron absolute rated filter, but consider pairing it with a UV disinfection system for comprehensive microbiological protection.
How often should I change a 5 micron sediment filter?
For most well water homes, every 3-6 months. The actual interval depends on your sediment load. When you notice a drop in water pressure at your fixtures, it's time to change the cartridge. Some homeowners with very clean wells go 6-9 months; others with heavy sediment change every 2-3 months. Keep a spare cartridge on hand so you can change it as soon as pressure drops.
Can a sediment filter remove bacteria from well water?
Standard sediment filters (5-50 micron) cannot reliably remove bacteria. Most bacteria are 0.2-5 microns, and even a 1 micron filter cannot guarantee bacterial removal because most sediment filters are nominal rated. For bacteria, you need either a UV disinfection system (which kills bacteria, viruses, and cysts) or a 0.2 micron absolute rated membrane filter. UV is the preferred method for whole-house well water disinfection.
What is the best micron rating for a whole house water filter?
5 micron. It's the industry standard for whole-house sediment filtration on well water. It balances filtration quality, flow rate, cartridge life, and cost. It catches particles 8 times smaller than what you can see with the naked eye, protects downstream treatment equipment, and typically lasts 3-6 months between changes.
Do I need a sediment filter if my water looks clear?
Yes. Particles smaller than 40 microns are invisible to the naked eye, but they still exist in most well water. These microscopic particles build up inside iron filter tanks, coat water softener resin, block UV quartz sleeves, and accumulate in water heaters. A 5 micron sediment filter protects all of your treatment equipment and fixtures from this invisible damage. Think of it as insurance for everything downstream.
What's the difference between polyspun and pleated sediment filters?
Polyspun (melt-blown) filters have a graded density structure: the outer layer catches larger particles, and the core catches finer particles. This gives them excellent dirt-holding capacity. Pleated filters have more surface area but capture particles at a single micron rating. For well water, we recommend polyspun because they handle variable sediment loads better and last longer between changes. Pleated filters work well for water with consistent, fine sediment.
Is 50 micron or 100 micron better for a spin-down filter?
For most wells, 50 micron is the better choice for a spin-down filter. It catches more particles while still allowing easy flushing. 100 micron is useful when you're dealing strictly with large sand particles and want absolute minimum flow restriction, but it lets a lot of medium-sized particles through. The Rusco spin-down filters come with interchangeable screens, so you can try both and see which works better for your well.
Does a sediment filter reduce water pressure?
All filters create some pressure drop (the water has to push through the filter media). A clean 5 micron filter in a 20" Big Blue housing typically causes a 4-6 PSI drop, which most homes don't notice. As the filter loads with sediment, the pressure drop increases until you change the cartridge. The 20" housing has less pressure drop than a 10" housing because the water flows through a larger surface area. If pressure is a concern, the 20" Big Blue kit is the better option.
Where should a sediment filter go in the treatment sequence?
Always first. The sediment filter protects everything downstream. The typical well water treatment sequence is: spin-down filter (before pressure tank) → pressure tank → Big Blue sediment filter (5 micron) → acid neutralizer → iron filter → water softener → carbon filter → UV light. The sediment filter goes between the pressure tank and the first treatment system. For more on treatment sequence, see our Complete Guide to Well Water Filtration Systems.
Keep Reading
- Best Sediment Filter for Well Water — our top picks compared side by side
- Big Blue Water Filter Guide — 10" vs. 20" housings, cartridge types, installation
- How to Choose a Sediment Filter — decision guide by sediment type, severity, and placement
- Sediment Filters for Well Water: Complete Guide
Aidan Walsh
Water Treatment Specialist, Mid Atlantic Water
Aidan has been diagnosing and solving residential water quality problems for over 30 years. He has personally installed thousands of well water treatment systems across the East Coast and talks with homeowners every day about their water. If you need help choosing the right sediment filter or micron rating for your well, call Aidan directly at 800-460-5810.