Sizing a Whole House Water Filter: Flow, Fixtures, and Tank Size

Add up the gallons-per-minute rating of every fixture that might run simultaneously. A typical shower is 2.0 to 2.5 gpm, a dishwasher 1.5 gpm, a washing machine 4.0 gpm at fill, and a kitchen sink 1.5 gpm.

A 2-bathroom home with one bathroom in use, the dishwasher running, and the kitchen tap on lands around 6 to 7 gpm peak. A 3 to 4 bathroom home with simultaneous showers lands at 9 to 12 gpm peak.

Pick a filter rated at or above your calculated peak. Almost every brand we cover offers a 7, 9, and 12 gpm size class. If you are between sizes, go up: an oversized filter runs cooler, lasts longer, and never bottlenecks pressure.

Carbon media is measured in cubic feet. A 1.0 to 1.5 cubic foot tank suits a 2 bathroom home, 2.0 cubic feet covers a 3 bathroom home, and 4.0 cubic feet is standard for the largest residential sizes.

Manufacturers rate carbon for roughly 1,000,000 gallons or about 10 years of city-water use, whichever comes first. Higher chloramine concentrations or a heavy iron load will shorten that.

Always pair the carbon tank with an upstream sediment pre-filter (5 micron is typical). The pre-filter is the cheap consumable that protects the expensive carbon bed.

All of the brands we recommend ship with a bypass valve. Install it. A bypass lets you isolate the filter for media swaps without shutting off water to the whole house, and it makes warranty service straightforward.

Plan for a drain within 20 feet if your system backwashes. Carbon tanks that backwash periodically need a drain line and an air gap to code.