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Is a 5-Micron or 20-Micron Filter Better?
A 5-micron filter removes finer particles than a 20-micron filter, but that does not automatically make it the better choice.
For most rainwater systems:
- A 20-micron filter works well as an early sediment filter. It catches larger dirt and debris while allowing relatively good flow.
- A 5-micron filter is better when you need finer sediment removal before another treatment stage, fixture, pump-fed appliance, or other equipment.
- In systems with a lot of sediment, using 20 microns first and 5 microns second can work better than putting a 5-micron filter directly on dirty water.
The right choice depends on what is in the water, how you plan to use it, and what equipment comes after the filter.
What Does Micron Rating Mean?
A micron is a very small unit of measurement. One micron is one-millionth of a meter.
A filter's micron rating describes the size of particles it is designed to catch.
A 20-micron filter has larger openings than a 5-micron filter. It lets smaller particles pass through.
A 5-micron filter has smaller openings, so it can catch finer particles.
Think of the two filters like screens:
- 20 micron = coarser screen
- 5 micron = finer screen
This mainly tells you about particle filtration. It does not tell you whether the filter removes chemicals, bacteria, viruses, or other contaminants.
5 Micron vs. 20 Micron at a Glance
| Feature | 20-Micron Filter | 5-Micron Filter |
|---|---|---|
| Particle removal | Coarser | Finer |
| Sediment holding | Usually handles heavier sediment better | Can clog faster with dirty water |
| Flow resistance | Generally lower | Generally higher |
| Best position | Early filtration | Later or finer filtration |
| Useful for rainwater | Yes | Yes |
| Makes rainwater safe to drink by itself | No | No |
Actual flow and filter life depend on the cartridge design, filter area, water quality, housing, and system pressure.
When a 20-Micron Filter Makes More Sense
A 20-micron filter is often the better starting point when your water carries visible sediment.
Roof runoff can bring small pieces of leaves, grit, pollen, insects, dirt, and roofing debris into a tank. Screens and first-flush systems can reduce this material, but some sediment can still reach the water supply.
A 20-micron cartridge can catch much of the larger suspended material without becoming clogged as quickly as a finer cartridge.
It can be useful for:
- Rain barrel or tank water used for general garden watering
- Prefiltration before a finer cartridge
- Systems where sediment loads are fairly high
- Protecting downstream filters from larger debris
- Reducing frequent replacement of finer cartridges
A 20-micron filter may also cause less restriction than a comparable 5-micron cartridge. That can matter in systems with weak gravity pressure or pumps that already have limited available flow.
However, micron size alone does not determine pressure loss. Cartridge construction and dirt loading matter too.
When a 5-Micron Filter Makes More Sense
A 5-micron filter is useful when you need to remove finer suspended particles.
Water passing through a 20-micron filter can still look slightly cloudy or contain particles too small for that filter to capture. A 5-micron cartridge provides another level of sediment control.
It may make sense when:
- You want finer sediment removal
- Water has already gone through a coarse prefilter
- You are protecting a downstream treatment stage
- Fine particles are causing problems with valves or fixtures
- A piece of equipment specifically requires filtration at that level
The tradeoff is that finer filtration can increase resistance to flow.
A 5-micron cartridge may also clog quickly if it receives untreated roof runoff containing a lot of dirt. As sediment builds up, water pressure or flow can fall.
This is one reason staged filtration is often useful.
Using 20 Microns and 5 Microns Together
You do not always have to choose one or the other.
A two-stage arrangement can look like this:
Tank → 20-micron filter → 5-micron filter → intended use or additional treatment
The 20-micron cartridge catches larger material first. The 5-micron cartridge then handles smaller particles.
This approach can help prevent the finer filter from doing all the work.
EPA material discussing small water treatment systems has similarly described staged cartridge filtration in which a coarser cartridge is followed by a finer cartridge.
More stages are not automatically better, though. Every cartridge creates some resistance. A gravity-fed rain barrel may have very little pressure available, so adding several fine filters can reduce flow dramatically.
Match the filtration setup to the water use rather than simply installing the smallest filter you can find.
Consider Nominal vs. Absolute Micron Ratings
Two filters marked "5 micron" may not perform exactly the same way.
A nominal rating generally means the filter removes a stated portion of particles around that size. The exact meaning depends on how the manufacturer defines and tests the cartridge.
An absolute rating describes a more controlled maximum pore size under specified conditions.
This distinction matters when filtration performance is important.
EPA guidance has specifically noted the importance of looking at absolute rather than nominal ratings when a filter is being selected for removal of certain microorganisms.
For ordinary sediment control in a rainwater system, a nominal cartridge may be suitable. For health-related treatment, do not assume that a micron number printed on a cartridge proves the required contaminant reduction.
Look for documented performance for the specific contaminant and application.
Which Is Better for Garden Irrigation?
For many simple garden watering systems, 20 microns may be more practical than 5 microns, especially when the main goal is keeping visible sediment out of hoses and general watering equipment.
But irrigation systems vary.
Small drip emitters can clog much more easily than an open hose or watering wand. Filter requirements also vary between irrigation components.
Check the filtration requirement provided by the irrigation equipment manufacturer. Do not choose a 5- or 20-micron cartridge based only on the assumption that finer is always safer.
Also watch your available pressure. A gravity-fed IBC tote may have much less pressure than a pumped irrigation system. A dirty fine filter can reduce that already-low flow further.
Which Is Better Before a Pump?
Understanding key facts about a better water filter, 5 micron or 20 micron helps verify which safety test should follow the initial result.
A coarse filter can help keep larger debris from reaching some pumps, but filter placement must be chosen carefully.
Putting a restrictive cartridge directly on a pump's suction side can reduce the water available to the pump. That can cause poor performance and, in some situations, contribute to pump problems.
Follow the pump manufacturer's requirements for:
- Suction-line size
- Strainer or prefilter type
- Maximum suction lift
- Required inlet conditions
- Minimum flow
- Filter placement
A pump system should not be designed around micron rating alone.
Often, large debris is controlled before the pump with appropriate screening or a strainer, while finer cartridge filtration is placed where the pump can provide enough pressure to push water through it.
Which Is Better Before UV Treatment?
A finer sediment filter is often used as part of pretreatment before ultraviolet treatment, but there is no universal rule that says every UV system needs exactly a 5-micron filter.
UV works by exposing microorganisms to ultraviolet light. Suspended material and poor water clarity can interfere with treatment.
Follow the UV manufacturer's specified water-quality and pretreatment requirements. Those requirements may cover more than particle size.
A 5-micron sediment cartridge also does not replace UV or another appropriate disinfection step.
Does a 5-Micron Filter Make Rainwater Drinkable?
No.
Neither a 5-micron nor a 20-micron sediment cartridge, by itself, can establish that collected rainwater is safe to drink.
CDC notes that collected rainwater can contain both germs and chemicals, even when the water looks clean. Contamination can come from the air, roof, gutters, piping, animals, and storage system.
Some bacteria are much smaller than 5 microns, and viruses are smaller still. EPA filtration information lists common bacteria at roughly 0.2 to 4 microns and viruses at roughly 0.004 to 0.1 micron.
Micron filtration also does not automatically remove dissolved chemicals.
CDC describes microfiltration as useful for parasites but notes that it is not dependable for complete bacterial removal and does not remove viruses or chemicals simply because the membrane is in the microfiltration range.
Drinking-water use therefore requires a whole-system approach. That can involve suitable collection surfaces, debris control, first-flush management, protected storage, appropriate treatment stages, regular maintenance, laboratory testing, and compliance with local requirements.
CDC recommends regular testing for germs and chemicals when collected rainwater is used for drinking, cooking, or bathing.
What About a First-Flush Diverter?
A sediment cartridge should not be expected to make up for poor collection practices.
A first-flush diverter sends the first portion of runoff from a storm away from the storage tank. This initial runoff can carry a concentrated load of dust, bird droppings, leaves, pollen, and other material that collected on the roof between rains.
CDC recommends considering a first-flush device as one way to improve collected rainwater quality.
Keeping larger contamination out of the tank can also reduce the amount of work required from downstream cartridge filters.
Watch Flow and Pressure
Moving from 20 microns to 5 microns can affect system performance.
The smaller filter openings create more resistance, especially as the cartridge fills with sediment.
You may notice:
- Lower faucet flow
- Weak irrigation performance
- Longer tank-filling times downstream
- Pump pressure changes
- More frequent cartridge replacement
Do not judge filter condition only by appearance. Some cartridges can collect enough material to restrict flow even when the outside does not look completely dirty.
A pressure gauge before and after a filter can be useful in larger pumped systems. The difference between those readings is called pressure drop. Increasing pressure drop can indicate that the cartridge is becoming restricted.
Follow the filter manufacturer's replacement guidance.
Choosing Between 5 and 20 Microns
Start with the intended water use and work backward through the system.
A practical approach is:
- Identify what you need to protect. A garden hose, drip system, pump, treatment unit, and household plumbing system may have different needs.
- Check equipment requirements. Use the filtration requirements supplied by the manufacturer of downstream equipment.
- Consider how dirty the incoming water is. Heavily sedimented rainwater can clog a fine cartridge quickly.
- Check available pressure and flow. Fine cartridges can be difficult to use in low-pressure gravity systems.
- Use staged filtration when it solves a real problem. A 20-micron cartridge followed by a 5-micron cartridge is often more practical than asking one fine filter to handle everything.
- Plan for maintenance. Filters that cannot be easily inspected and changed often end up being neglected.
For basic sediment removal, 20 microns is usually the more forgiving first stage. When finer sediment control is needed, 5 microns is the stronger finishing stage.
Neither rating should be treated as proof of safe drinking water.
Frequently Asked Questions
Is 5 micron finer than 20 micron?
Yes. A 5-micron filter has finer filtration than a 20-micron filter and can capture smaller suspended particles.
Will a 5-micron filter clog faster?
It can. When the incoming water contains a lot of sediment, a finer cartridge often collects material faster and may develop more flow restriction. Using a coarser prefilter first can help.
Can I put a 20-micron filter before a 5-micron filter?
Yes. This is a common staged-filtration approach. The 20-micron cartridge catches larger particles before the water reaches the finer 5-micron cartridge.
Is a 20-micron filter enough for rainwater?
It may be enough for some non-potable uses where the main goal is sediment control. Non-potable means water that is not intended for drinking. Requirements can be different for drip irrigation, appliances, household reuse, and additional treatment systems.
Does a 5-micron filter remove bacteria?
Do not assume that it does. Many bacteria can be smaller than 5 microns, and filter ratings vary in how they are defined. Choose treatment based on documented performance for the specific contaminant rather than the micron number alone.
Does a 5-micron filter remove viruses?
No ordinary 5-micron sediment filter should be relied on for virus removal. Viruses are far smaller than 5 microns.
Should I use the smallest micron filter possible?
Not necessarily. A very fine filter can reduce flow and clog quickly. Use the filtration level required for your water use and downstream equipment, with coarser pretreatment when needed.
