# Whole-house water filtration filter

> A whole-house filtration filter sits on the main line and treats every fixture. See the housing sizes, stage order, flow ratings, and installed costs.

Canonical: https://watertreatmentpro.com/whole-house-water-filtration-filter/

Last updated: 2026-11-09

A whole-house water filtration filter is a point-of-entry housing on the main supply line, so every shower, tap, and appliance receives filtered water. It costs $500 to $1,800 installed and uses 4.5 inch cartridges rated to pass 8 to 15 gallons per minute.

## Housings and Flow

The housing size is set by the flow, not by the cartridge price. A standard 2.5 inch housing passes 4 to 6 gpm, which is fine for a single fixture and inadequate for a house.

| Housing | Cartridge | Practical flow | Pressure drop |
|---|---|---|---|
| 2.5 x 10 | Standard | 4 - 6 gpm | 2 - 5 psi |
| 4.5 x 10 | Big blue | 8 - 12 gpm | 1 - 3 psi |
| 4.5 x 20 | Jumbo | 12 - 20 gpm | 1 - 3 psi |

A whole-house system built on a 2.5 inch housing will choke the showers no matter which cartridge is inside. Velocity through the media rises, pressure drop climbs, and the household blames the municipal supply.

The 4.5 by 10 inch housing is the practical default for a three-bathroom home. The 20 inch version adds media volume and change interval, at the cost of wall space and a taller cartridge.

## The Stage Order

Two stages cover most municipal water.

1. **Sediment, 10 or 20 micron.** Takes grit, rust, and turbidity. Protects the carbon block behind it.
2. **Carbon block.** Removes chlorine, taste, and odour. Protects resin, membranes, and the UV sleeve if fitted.

Reversing them is a common error. Carbon first loads with grit and blinds in weeks, while the sediment cartridge behind it stays clean and does nothing useful.

A third stage is added when the water calls for it: catalytic carbon for chloramine, a specialty media for a specific metal, or a second carbon block for taste polish. Each stage adds pressure drop, so the total has to stay inside the budget.

## What It Removes

| Contaminant | Sediment | Carbon |
|---|---|---|
| Sand and grit | Yes | No, nominal only |
| Rust particles | Yes | No |
| Chlorine | No | Yes |
| Taste and odour | No | Yes |
| Chloramine | No | Catalytic carbon only |
| Hardness | No | No |
| Nitrate | No | No |
| Bacteria | No | No |

The last three rows are the boundary. A whole-house filter is not a softener, not a reverse osmosis system, and not a disinfectant.

Households often buy a whole-house filter expecting softer water and are disappointed. The filter improves taste and protects plumbing from sediment, and it does nothing about scale. If hardness is above 7 GPG, the softener is a separate purchase.

## What It Costs

A two-stage 4.5 inch system installed runs $700 to $1,200. Cartridges cost $20 to $40 for sediment and $35 to $70 for carbon.

Annual arithmetic: sediment three times a year at $25 is $75; carbon twice a year at $50 is $100. Total $175 per year.

Ten years: $900 installed plus $1,750 in cartridges equals $2,650, or $265 per year. That is the estimate to compare against a dealer package, which usually bundles service and salt.

## Installation Essentials

The system needs a bypass, a level mounting, and enough pipe to cut in. A bypass lets you change cartridges without shutting off the house, and it costs $60 to $200 in parts.

Pipe material sets the labor. PEX and copper cut and rejoin quickly. Galvanized steel usually means replacing a section, which adds an hour and a few fittings to the job. A plumber quoting without seeing the pipe is quoting the easy case.

Mount the housings at chest height with 12 inches of clearance below for cartridge removal. A housing mounted too low means draining the cabinet or lying on the floor every change.

Put the system before the water heater. Filtering hot water degrades carbon and shortens cartridge life, and the heater does not need filtered water anyway.

## Five Steps to Choose

1. **Test the water** and identify what needs removing.
2. **Measure peak flow** from simultaneous fixtures.
3. **Choose the housing size** from the flow.
4. **Set the stage order** sediment then carbon.
5. **Confirm the bypass and clearance** before installing.

## Maintenance

Sediment every 3 to 6 months, carbon every 6 to 12 months. Write the date on the housing.

If pressure drops early, the sediment stage is loading faster than the rating assumed, which means the water carries more particulate than expected. A spin-down pre-filter ahead of the cartridges is the fix, and it pays for itself in cartridge life.

Keep one spare of each cartridge on the shelf. A housing that sits empty for a week because nobody ordered a replacement is worse than no filter, since the bypass is open and the house is on raw water. The spare costs $50 and removes the excuse.

## Buying Notes

Housings are commodity parts and cartridges are the product. A $40 housing with a certified $25 cartridge outperforms a $120 housing with an uncertified $10 cartridge, and the difference is invisible on the shelf.

Look for NSF/ANSI 42 on the carbon cartridge and 53 if a health claim is made. A "taste and odour" cartridge is doing 42 work whether or not the box says so, and a cartridge claiming lead reduction without a 53 listing is claiming something it has not demonstrated.

Buy the housing with a wrench included, or buy one that takes a standard wrench. Some proprietary housings need a special tool that costs as much as the cartridge.

For the full-house overview, see [whole house water filter](https://watertreatmentpro.com/whole-house-water-filter/) and [how a whole house filter works](https://watertreatmentpro.com/how-does-a-whole-house-filter-work/). For the price breakdown, [whole house water filter cost](https://watertreatmentpro.com/whole-house-water-filter-cost/) covers labor and parts, and [water filter system](https://watertreatmentpro.com/water-filter-system/) covers the staging logic.