The general rule is that a sediment filter should always be installed before a carbon filter. Sediment filters prolong the lifespan of other filters by removing all the dirt and large particles that could cause clogging.
You should only install a carbon filter first – before the sediment filter – if it’s a backwashing system and the required backwashing flow rate is higher than the sediment filter’s output flow.
Installing Sediment or Carbon Filter First?
Sediment or carbon filter – it can be tricky to decide which one goes first, so let’s shed some light in the dark.
When the Sediment Filter Goes First
Sediment filters usually go first to prevent sediments from clogging other water system components, like softeners and water heaters. That’s why sediment filters are usually referred to as “pre-filters”.
As for water filtration, when sediment filters come first, they trap sediment and dirt that could interfere with other parts of the treatment process. Consequently, they prolong the lifespan of subsequent filter stages, such as carbon filters.
If, on the other hand, a carbon filter would be installed first in line, there’d be nothing to protect it from dirt. Depending on your water quality, it could get clogged in no time and the filter media would go bad. The result: Not only reduced water pressure but the carbon media would eventually stop removing contaminants altogether.
When the Carbon Filter Goes First | Backwashing Rates
The only case where a carbon filter may need to be installed before the sediment filter is if the former is a backwashing filter.
From time to time, a backwashing filter reverses the flow of water to clean its filter bed. And if placed after a sediment filter with a low output flow rate, a backwashing carbon filter could not flush its filter bed properly. This would affect performance significantly and reduce the overall filter service life.
Simply put, you must place a backwashing filter before any other filtering stage that has a lower output flow rate than what’s required for backwash. Which means that, you can put a sediment filter before a backwashing carbon filter if its flow rate is higher or equal to that of the carbon filter backwash.
The scenarios we described above only apply to whole house/point-of-entry water filters.
Carbon filters can only come first in whole house systems. In point-of-use water filters like under sink reverse osmosis systems, the sediment filters always come first.
What’s a Carbon Water Filter and How Does It Work?
Carbon water filters use activated carbon as a medium for filtration. Activated carbon is obtained from coconut shells, wood, or charcoal and has been treated to become highly porous with a large surface area.
When used for filtration, activated carbon adsorbs impurities into its surface and traps them in its pores like a sponge. The adsorption process is quite similar to how a magnet attracts iron filings. This filtration method makes carbon filters highly effective in removing organic compounds, chlorine, pesticides, trihalomethanes, and other chemical impurities from water. It also improves the taste of water and eliminates odor.
Furthermore, carbon filters are of two types:
Carbon blocks
Granular activated carbon
While both types have similar levels of effectiveness, granular activated carbon allows water to pass more freely. Hence it’s more suitable for systems that demand higher water pressure.
What’s a Sediment Filter and How Does It Work?
Sediment filters are systems designed to remove solid particles like debris, dirt, sand, and rust bits from water. These sediments can come from corroded plumbing, stormwater runoff, sand in groundwater, and many other sources.
Sediment filters remove them through a mechanical process that usually involves passing the water through screen-like cartridges.
Sediment filters are available in different types, each tailored to tackle various sizes of contaminants. Examples are pleated filters for large particles like sand and string-wound filters removing fine silt.
What Is a Micron Rating?
Most sediment filters come with a micron rating labeled on their package. It’s important to consider them before purchasing since they determine the filter’s effectiveness. But first, you need to understand what they mean.
A micron is a unit of measurement used to describe the pore size in a filter media. A sediment filter can have pores the size of as little as 0.5 microns and as large as 100 micron. Any particles larger than the indicated size (micron rating) will not pass through the filter but get stuck.
In other words, micron ratings indicate the size of contaminants a filter can remove. For example, a filter with a very low micron rating has tiny pores that will prevent almost all contaminants from passing through. A filter with a higher micron rating will only trap large impurities.
What’s more, micron ratings are classified into two types: Nominal and absolute.
Nominal ratings are given to filters that have been tested and proven to remove a specific percentage, usually70-80%, of contaminants of a certain size. For example, say a filter has a nominal rating of 60 microns. It means the filter will remove up to 80% of contaminants with a size of 60 microns or higher.
On the other hand, absolute micron ratings give a more reliable metric since they indicate that a filter can remove all contaminants of a particular size. So an absolute rating of 10 microns means the filter will remove all contaminants down to that size.
Lastly, here are some examples of whole house sediment filter micron ratings:
100 microns – filters large particles like sand
50 microns – fine sand, hair, dust, and other contamination that the naked eye can still see
25 microns – smaller particles invisible to humans
5 microns – silt, and sometimes cysts and bacteria
If you have any questions about carbon or sediment filter first please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
Alex is a content writer with an affinity for research and a methodical attention to detail. Since 2020, she has fully immersed herself into the home water treatment industry only to become an expert herself. Alex has been using water filters and similar products for years which has gained her lots of hands-on experience.
Learn more about Alex and the rest of the BOS Team.
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Leave a Comment:
James says
June 2, 2023
We have an inline sediment filter (5 microns) after our pressure tank and prior to our carbon tank. We change this filter every 5-8 weeks, and it shows a bit of mineral deposits, but no particulate matter. Unfortunately, we are getting a silty black particulate down the line from our carbon tank. This shows up with reduced flow in faucets, and water boiler issues. Several times we’ve had to pull shower heads off after our carbon tank did its periodical recycle. We’ve cycled our water boiler (wall mount on demand) and gotten an inch or so of black silt out of it. It appears this silt is somehow coming from the carbon tank, rather than from our well and through our sediment filter. How is this possible?
Hi James,
It’s either that the black silt is too small for the sediment filter to catch, or it’s carbon media breaking down. I’m assuming it’s the latter!
