What is a whole-house water filtration system?
Updated August 2026
Whole-house water filtration is a point-of-entry setup that treats every gallon coming into the house, most often a sediment pre-filter followed by a carbon stage that strips chlorine, taste, and odor. Point of entry is the distinction that matters. An under-sink or countertop filter cleans water at one tap; this equipment sits ahead of the entire plumbing system, so the shower, the washing machine, the ice maker, and the water heater all receive treated water. A typical two-stage build passes 7 to 15 gallons a minute, enough to serve two or three fixtures at the same time.
Where it is
Study the first 6 feet of pipe after the meter and the main shutoff, before the line branches toward the water heater. A cartridge system shows up as one or two blue or clear housings, 10 or 20 inches tall, hanging on a bracket. A media system looks like a fiberglass tank 9 to 13 inches across and 48 to 60 inches tall with a control head on top. Both want three things nearby: a bypass loop so the house keeps water while you service the filter, 6 to 8 inches of clearance underneath to drop the sump, and a drain for backwash if the media self-cleans. Outdoor hose bibbs are normally teed in ahead of the filter, because filtering the lawn wastes cartridges.
What it does
The sediment stage does the unglamorous work, catching sand, rust flakes, and pipe scale down to about 5 microns before any of it scores faucet cartridges, plugs aerators, or jams appliance inlet screens. The carbon stage handles what you taste and smell, mainly chlorine and chloramine, and it protects softener resin and rubber seals downstream. Specialty media go further: catalytic carbon or greensand for iron and sulfur odor, calcite for acidic well water, and media certified to NSF/ANSI 53 for lead or PFAS. The limits deserve equal billing. Filtration does not soften water, so scale keeps forming unless a softener follows it, and it does not disinfect, which is the job of a UV lamp on well water. Neglect is the standard failure, and a loaded 5-micron cartridge can swallow 15 to 25 psi. The first symptom is weak showers everywhere at once rather than at one fixture.
Maintenance
Sediment cartridges come out every 3 to 6 months at $15–40 each, sooner on well water or after crews work on the street main (whole-house filter intervals). Carbon block cartridges run 6 to 12 months. A backwashing carbon tank holds its media 5 to 10 years and costs $300–700 to re-bed. Pressure is the honest trigger, so mount a gauge before and after the housing and change the element at a 10 to 15 psi spread instead of guessing at a calendar. Any reverse osmosis unit or UV lamp downstream keeps its own clock (RO filter changes and UV bulb replacement), and complete systems generally serve 10 to 15 years before the head and housings give out (system lifespan).
What it costs to replace
A replacement whole-house water filtration system runs $800–3,000 installed for a two-stage system, plus $60–150 a year in cartridges.
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Frequently asked questions
Do I still need an under-sink filter if I have a whole-house system?
They solve different problems. The point-of-entry system protects fixtures and appliances and gives you chlorine-free showers, which is most of the comfort benefit. A reverse osmosis unit at the kitchen sink, $200–600 installed, takes drinking water to a much finer standard by pushing it through a membrane that a whole-house filter cannot match at 10 gallons a minute. Plenty of homes run both, with the whole-house filter feeding and protecting the RO membrane.
Does a whole-house filter soften hard water?
No. Carbon and sediment media capture particles and dissolved chemicals, and they leave calcium and magnesium untouched, so scale keeps building in the water heater and on the showerhead. Softening requires ion exchange in a resin tank with a salt supply. When both go in, the usual order is sediment first, carbon second, softener last, so the resin never sees chlorine. Budget $800–2,500 for the softener on top of the filtration.
What happens if I never change the cartridge?
Three things, in order. Pressure across the house falls as the element loads up. Then water channels through the path of least resistance and exits mostly unfiltered. Finally the housing becomes its own project, because a sump torqued in place for three years often needs a $15–25 wrench and real force to break loose. A saturated carbon bed can seed bacteria too, which is why 12 months is a hard ceiling on carbon.
Will one of these remove lead or PFAS?
Only if the specific media carries certification for that contaminant. Look for NSF/ANSI 53 on a filter or 58 on a reverse osmosis system, listed for the contaminant by name, and treat any unlabeled claim as marketing. Start with a test rather than a guess: a certified lab panel runs $30–150 depending on the contaminant list, and utility customers get an annual water quality report for free that names what is already in the supply.