Sediment filters
The short answer
A sediment filter removes suspended particles — sand, silt, rust and scale — by physically straining them out. It belongs first in the treatment train because everything downstream is more expensive and more easily damaged. It is the cheapest stage to run and the one most worth having.
- Where it goes
- First, where the supply line enters the house.
- Typical cost
- $60–$400 installed, plus $20–$80 a year in cartridges
What it removes — and what it doesn't
This is the part sales pages are vaguest about, so it is worth being blunt. No single stage treats everything, and buying the wrong one for your water is the most common way people end up with expensive equipment that changes nothing.
Removes
- Sand, grit and silt
- Rust flakes and pipe scale
- Oxidised iron and manganese particles
- Turbidity that would otherwise shield bacteria from UV
Does not remove
- Anything dissolved — hardness, iron in solution, nitrate
- Bacteria or viruses (they pass straight through)
- Tastes, odours or colour
- Chemicals of any kind
The three types, and when each makes sense
Sediment filtration comes in three practical forms, and choosing badly is the difference between a filter you change twice a year and one you fight with every month.
- Spin-down separators — a mesh screen in a clear housing with a flush valve at the bottom. Handles coarse sand and grit, and you flush it rather than replacing anything. Ideal as a first stage where the well produces a lot of material.
- Cartridge filters — a replaceable element in a housing, rated in microns. The standard choice for fine material. Cheap to buy, ongoing cost in cartridges.
- Backwashing media filters — a tank of graded media that cleans itself on a schedule. More expensive up front, no cartridges to buy, and the right answer for high flow or heavy sediment loads.
Choosing a micron rating without killing your pressure
The instinct is to fit the finest filter available, on the reasoning that finer must be better. It is the most common mistake made at this stage and it produces a filter that clogs in weeks, drops household pressure, and eventually gets removed in frustration.
A filter's micron rating is the particle size it captures. Finer ratings capture more, but they also block faster and restrict flow more. The right rating is the coarsest one that produces clear water, not the finest one you can buy.
Where sediment is heavy, staging works far better than a single fine filter: a spin-down or a 50-micron cartridge first, then a 5-micron behind it. The coarse stage takes the bulk of the load and the fine stage lasts many times longer than it would alone.
- 50–100 micron — visible sand and grit. Usually a spin-down separator.
- 20–30 micron — general-purpose first stage for most wells.
- 5–10 micron — fine silt, and protecting a UV lamp or an RO membrane.
- 1 micron or below — only where something specific downstream requires it. Expect frequent changes.
Where it goes
First, after the pressure tank and before everything else. Its whole job is protecting what comes after it, so anything installed upstream of the sediment filter is unprotected.
One exception is worth knowing: if you have an iron filter or another oxidising stage, that stage converts dissolved iron into particles, which then need catching. A second sediment filter after the oxidising stage is normal and is not a duplicate of the first.
Fit the housing where you can actually reach it. A filter you have to empty a cupboard to change is a filter that does not get changed.
Knowing when to change it
The honest answer is that a schedule is a poor guide, because how fast a cartridge loads depends entirely on how much your well produces. Pressure is the real indicator.
The cheap and reliable method is a pair of pressure gauges, one either side of the filter housing. When the difference between them reaches about 10–15 psi, the cartridge is done. A clear housing helps too, though a filter can be well past its useful life before it looks dirty.
A gradual, whole-house drop in pressure over weeks is very often nothing more than a loaded sediment cartridge. It is worth ruling out before suspecting the pump.
Cost figures are planning ranges for typical residential equipment, gathered from published pricing. They are not quotes, and installed cost varies widely with your plumbing, your water and your region. Get written quotes before committing.
Frequently asked questions
- Does a sediment filter remove bacteria?
- No. Bacteria are far smaller than any practical sediment filter's rating and pass straight through. Sediment filtration does help UV disinfection work by removing the particles that shield organisms from the lamp, but it does not itself remove them.
- What micron sediment filter do I need for well water?
- Start at 20–30 micron for a general-purpose filter and go finer only if the water is still cloudy. Fit 5 micron or below where you are protecting a UV lamp or an RO membrane. Finer is not better — it clogs faster and costs pressure.
- Does a sediment filter reduce water pressure?
- A clean one causes a small drop of a few psi. A loaded one causes a large drop, and that is exactly how you know it needs changing. Gauges either side of the housing turn this into a measurement rather than a guess.
- Do I still need a sediment filter if I have a softener?
- Yes, and more so. Sediment fouls softener resin and shortens its life, so the filter is protecting a much more expensive component. Sediment filtration always goes ahead of a softener.