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A 5-micron water filter removes finer particles than a 20-micron filter, but that does not automatically make it the better choice. A 5-micron filter can give cleaner-looking water, while a 20-micron filter usually handles heavier sediment with less clogging and better flow.
For many rainwater systems, the best setup is not choosing one or the other. It is using them in stages: a 20-micron filter first, followed by a 5-micron filter when finer sediment removal is needed.
What Does Micron Rating Mean?
A micron is a very small unit of measurement. One micron is one-thousandth of a millimeter.
The micron rating of a filter describes the size of particles it is designed to catch.
In simple terms:
- A 20-micron filter catches larger sediment.
- A 5-micron filter catches smaller sediment.
- Smaller micron numbers mean finer filtration.
This rating mainly tells you about particle size. It does not tell you everything the filter can remove.
Two filters with the same micron number can also perform differently depending on their material, construction, and whether their rating is nominal or absolute.
Nominal vs. Absolute Micron Ratings
This difference matters when comparing filters.
A nominal rating means the filter removes a stated percentage of particles around that size. Some particles larger than the rating may still pass through.
An absolute rating sets a much stricter limit on the largest pore size.
The CDC notes that an absolute 1-micron filter has pores that are 1 micron or smaller, while a nominal or mean 1-micron filter can have some larger pores.
For ordinary sediment removal, nominal cartridges are common. For treatment where a specific particle or organism reduction is important, look at the filter's actual performance claims rather than relying only on the micron number.
5 Micron vs. 20 Micron at a Glance
| Feature | 5-Micron Filter | 20-Micron Filter |
|---|---|---|
| Filtration | Finer | Coarser |
| Small sediment removal | Better | Less effective |
| Heavy sediment handling | Clogs sooner | Usually better |
| Flow resistance | Usually higher | Usually lower |
| Filter life in dirty water | Often shorter | Often longer |
| Good as first sediment stage | Sometimes | Often |
| Good as a polishing sediment stage | Yes | Less effective |
The exact flow and filter life depend on the cartridge design, filter housing, water pressure, and how much dirt is in the water.
When Is a 20-Micron Filter Better?
A 20-micron filter is often the better first filter when the water carries visible or relatively large sediment.
In a rainwater system, this may include:
- Fine grit
- Rust flakes
- Tank sediment
- Small pieces of organic debris
- Material carried through gutters and downpipes
Because its openings are larger, a 20-micron filter usually allows water to pass more easily than a finer cartridge of similar construction.
That can be useful when feeding:
- Garden irrigation
- Pumps
- Larger storage systems
- Hose outlets
- Additional filters
It can also protect a finer downstream filter from becoming packed with sediment too quickly.
For example, water leaving a rainwater tank might first pass through a 20-micron sediment filter. A 5-micron cartridge farther downstream can then handle the smaller material.
When Is a 5-Micron Filter Better?
Choose a 5-micron filter when you need finer sediment removal and the water is already reasonably free of large debris.
It can help catch smaller particles that would pass through a 20-micron cartridge.
A 5-micron stage may make sense before equipment that works better with low-turbidity water, or simply when you want better removal of fine suspended sediment.
It can also be useful as part of a multi-stage treatment system.
The drawback is that finer filters can clog faster.
If you put a 5-micron cartridge directly on very dirty rainwater, it may collect large and small particles at the same time. The cartridge can load up quickly, causing lower flow and greater pressure loss.
Why a 20-Micron Filter Followed by a 5-Micron Filter Often Works Better
Staged filtration divides the work between filters.
Water flows through the coarser filter first:
Rainwater tank → 20 micron → 5 micron → next treatment stage or intended use
The 20-micron cartridge catches the larger sediment. The 5-micron cartridge then handles smaller particles.
This arrangement can provide several benefits:
- Better overall sediment removal
- Less rapid clogging of the 5-micron cartridge
- More stable flow
- Longer service intervals for the finer filter
- Better protection for downstream equipment
You do not always need two stages.
For simple garden watering, for example, a coarse sediment filter may be enough if it protects the pump and irrigation equipment adequately.
A household reuse system or more complex treatment train may benefit from several filtration and treatment stages.
Does a 5-Micron Filter Reduce Water Pressure?
It can.
Any filter creates some resistance to water flow. That resistance normally increases as:
- The filter becomes finer
- Flow demand increases
- The cartridge becomes dirty
- The cartridge surface area decreases
- The housing or connections are too small
Alongside comparing five- and 20-micron filtration, understand installation details that support reliable daily use.
A clean 5-micron filter in a properly sized housing may cause little noticeable trouble. But the same cartridge can create a substantial pressure drop after it fills with sediment.
This matters especially with pumps.
Do not choose a filter cartridge based only on its micron rating. Make sure the housing, cartridge, pipe size, and expected flow are suitable for the pump and fixtures connected to the system.
What Micron Filter Is Best for Rainwater?
There is no single micron rating that works for every rainwater system.
Start with the intended use.
For garden irrigation, the goal may mainly be protecting pumps, valves, and emitters from sediment. A relatively coarse filter can sometimes do that without unnecessary flow restriction.
For toilet flushing or other household non-potable uses, finer sediment filtration may help keep water clearer and protect plumbing equipment.
For systems with UV treatment, good prefiltration is especially important because suspended particles can interfere with UV treatment. The CDC notes that UV treatment works better when water is filtered beforehand.
The correct filter sequence depends on the condition of the collected water and the requirements of the equipment downstream.
Good rainwater management also starts before the cartridge filter. Keeping gutters reasonably clean, screening larger debris, managing the first portion of dirty roof runoff where appropriate, and limiting sediment entering the tank can reduce the load on later filters.
Is 5 Micron Enough to Make Rainwater Safe to Drink?
No.
A 5-micron sediment filter should not be treated as a complete drinking-water treatment system. Neither should a 20-micron filter.
Roof runoff can contain microorganisms, chemicals, animal waste, metals, and other contaminants that cannot be assessed or controlled by sediment filtration alone.
The CDC recommends testing water from rainwater collection systems for harmful germs and chemicals and choosing treatment based on what needs to be removed. Different filter and treatment technologies address different contaminants.
If rainwater is intended for drinking, treat it as a whole-system decision involving suitable collection, prefiltration, appropriate treatment, current laboratory testing, ongoing maintenance, and applicable local requirements.
A smaller micron number by itself does not prove that water is potable, meaning suitable for drinking.
How to Choose Between 5 and 20 Microns
Consider what is happening in the whole system rather than looking only at the filter number.
A 20-micron filter is usually the stronger choice when:
- There is a significant sediment load.
- You need a first-stage filter.
- Maintaining flow is important.
- You want to protect a finer downstream cartridge.
- The water is being used for an application that does not require very fine sediment removal.
A 5-micron filter is usually the stronger choice when:
- The larger sediment has already been removed.
- Fine suspended particles are causing problems.
- Downstream equipment benefits from cleaner water.
- You are adding a polishing sediment stage.
- The system can tolerate the additional flow resistance.
If both large and fine particles are present, installing the 20-micron filter before the 5-micron filter is often more practical than asking the 5-micron cartridge to do everything.
Do Not Forget Filter Maintenance
Even a well-sized filter needs maintenance.
Watch for:
- Falling water pressure
- Lower flow from taps or hoses
- Pumps running differently than normal
- Visible discoloration in the cartridge
- Sediment appearing downstream
Follow the cartridge manufacturer's replacement or cleaning instructions.
Do not assume a filter is still working correctly simply because water continues to flow through it. A clogged filter can restrict the system, while a damaged or poorly fitted cartridge may allow sediment to bypass it.
Filter housings, seals, and O-rings also need inspection. A good cartridge cannot work properly if water can travel around it instead of through it.
Frequently Asked Questions
Is 5 micron finer than 20 micron?
Yes. A 5-micron filter is finer and can catch smaller particles than a 20-micron filter.
Will a 5-micron filter clog faster?
Usually, especially when the water contains a lot of sediment. Because it captures smaller particles, more material can collect in the cartridge. Using a coarser prefilter can reduce this problem.
Should I use a 20-micron filter before a 5-micron filter?
Often, yes. The 20-micron stage removes larger sediment first, reducing the amount of material reaching the finer 5-micron cartridge.
Is 20 microns enough for rainwater?
It may be enough for some sediment-control jobs, such as protecting certain pumps or irrigation equipment. It is not automatically enough for every use, and it should not be considered complete treatment for drinking water.
Can a 5-micron filter remove bacteria?
Do not assume that an ordinary 5-micron sediment cartridge makes water microbiologically safe. Filter performance depends on pore rating, construction, and validated treatment claims. The CDC recommends choosing treatment specifically for the germs or chemicals that need to be controlled.
Does a smaller micron filter always give better water?
It gives finer particle filtration, but it can also reduce flow and clog faster. The smallest micron rating is not always the most practical filter for the job.
Can I go directly from 20 microns to 5 microns?
Yes. A 20-micron-to-5-micron sequence is a common and sensible sediment-filtration arrangement when the first cartridge removes enough material to protect the second. Very dirty water may benefit from even coarser screening or filtration before these stages.
