How to Change a Whole-House Water Filter (4 Steps + Timing)

TL;DR: Whole-house water filters typically need cartridge replacement every 3-6 months, though sediment-heavy well water may shorten that to 6-8 weeks. The process takes 20 minutes: shut the inlet valve, relieve system pressure, unscrew the housing, swap the cartridge, re-seat the O-ring, and check for leaks. Reduced flow or visible sediment on the old cartridge are better timing signals than the calendar.

_Last reviewed: July 2026 · 6 min read_

If your water pressure has dropped or you've noticed grit in the washing machine, the first suspect is your whole-house filter. These units sit on the main line where water enters the house and catch sediment, rust, and particulate before it reaches faucets, appliances, and heaters. Unlike under-sink filters that handle one tap, a whole-house cartridge processes every gallon used in the home—so it clogs faster and needs regular swaps.

Okoniq Property Hub keeps a maintenance log for your filter schedule, attachment photos of the housing model, and notes on cartridge part numbers so you never scramble to remember which size fits.

When do you actually need to replace the cartridge?

Manufacturer labels often print "replace every 3-6 months," but real-world timing depends on sediment load and daily volume. A household on municipal water with light particulate might stretch six months; well water with iron or sand can choke a 5-micron cartridge in two months. Watch for three signs: a 10-15% drop in shower pressure, rust stains reappearing in toilets, or visible brown sediment on the old cartridge when you pull it. If you track water usage in Okoniq, a sudden spike in flow complaints from tenants or family members is a concrete indicator.

Sediment filters (5-20 micron pleated or spun polypropylene) are the most common whole-house type and handle dirt, rust, and sand. Carbon-block cartridges tackle chlorine taste and some organics but flow slower and cost more per change. Combination housings use a sediment pre-filter followed by carbon; the sediment stage usually clogs first. Check the filter housing label for the cartridge model number—common sizes are 10×2.5″, 10×4.5″, and 20×4.5″.

What tools and parts do you need before you start?

Gather the replacement cartridge (verify the micron rating and diameter match your housing), a filter wrench or strap wrench for the sump, a bucket to catch water, plumber's grease for the O-ring, and a rag. Most sump housings hold 1-2 quarts of water, so size your bucket accordingly. If your housing is older than five years, buy a spare O-ring—they harden and crack, and a $3 part beats a flooded utility room. Some filter housings include a pressure-release button on top; if yours doesn't, you'll relieve pressure manually by opening the sump a quarter-turn.

Before touching the housing, shut the inlet valve (usually a ball valve immediately upstream of the filter) and open a cold-water faucet on the lowest floor to drain downstream pressure. This step prevents a geyser when you unscrew the sump. Place your bucket under the housing, then use the wrench to turn the sump counterclockwise. The first quarter-turn will release trapped pressure and water—let it drain into the bucket before removing the sump completely.

How do you swap the cartridge and re-seal the housing?

Pull the old cartridge straight up off the center post. Inspect it for sediment color and texture; uniform brown or orange rust is normal, but black slime suggests bacterial growth (consider a UV stage or chlorine shock if you're on a well). Dump the spent cartridge in the trash—most polypropylene and cellulose filters are not recyclable. Wipe the inside of the sump and the rim with a damp rag to remove grit that could compromise the O-ring seal.

Check the O-ring for nicks or flat spots; if it looks compressed or brittle, replace it now. Apply a thin bead of food-grade silicone or plumber's grease around the ring—this helps it seat evenly and slide during tightening. Drop the new cartridge onto the center post, making sure it sits flush at the base. Thread the sump back onto the cap by hand, turning clockwise until snug, then give it a final quarter-turn with the wrench. Over-tightening can crack the housing; stop when you feel firm resistance. For guidance on other plumbing checks that prevent leaks, see how to diagnose a ceiling water stain.

How do you test the system and purge trapped air?

Open the inlet valve slowly. Water will fill the housing and you'll hear gurgling as air purges through the cartridge. Watch the sump base for drips—if you see water beading at the O-ring, shut the valve, release pressure, and re-seat the sump with a bit more grease on the ring. Once the housing is dry for 30 seconds under full pressure, open the cold tap you used earlier and let it run for two minutes to flush carbon fines or loose sediment from the new cartridge. Expect cloudy or gritty water for the first 15-20 seconds; this is normal and clears quickly.

Mark the replacement date on the housing with a permanent marker or log it in Okoniq with a photo of the new cartridge. If you manage a rental, attach the receipt and part number to the property file so the next landlord or maintenance tech knows exactly what to order. Whole-house filters protect appliances and fixtures from abrasive particulate, so staying on schedule can add years to water heaters and washing-machine valves. For broader seasonal plumbing tasks, see closing a seasonal home for winter.

What if you have a two-stage or UV system?

Two-stage housings use a sediment cartridge in the first canister and carbon in the second. Change them both during the same service call, starting with the upstream sediment unit so you don't flush debris into the fresh carbon filter. The process is identical: shut the valve, relieve pressure, swap cartridge, grease the O-ring, tighten, test. UV units downstream of the filter housings need annual bulb replacement and quarterly quartz-sleeve cleaning, but those steps happen separately from cartridge swaps. If you see persistent cloudiness after changing a sediment filter, the issue may be air in the lines or a clogged drain elsewhere creating back-pressure.

FAQ

How long does it take to change a whole-house water filter cartridge?

Plan on 20 minutes from valve-shut to final leak check. First-time swaps take 30 minutes while you locate the wrench and figure out the O-ring orientation; repeat jobs are faster once you know the housing quirks.

Can you over-tighten the filter housing and crack it?

Yes—plastic housings crack if you reef on them with a pipe wrench. Hand-tighten until snug, then add a quarter-turn with a strap wrench or the supplied plastic wrench. If the O-ring is greased and seated properly, that's enough torque to seal.

What micron rating should you use for well water with sediment?

Start with a 20-micron sediment filter if you see visible sand or grit; once that's handling the coarse load, add a 5-micron stage downstream for finer particles. Jumping straight to 5 micron will clog in weeks and cost more in cartridges.

Do you need to sanitize the housing between cartridge changes?

Not routinely, but if you see black slime or smell sulfur, wipe the sump with diluted bleach (1 tablespoon per quart of water) and rinse thoroughly before installing the new cartridge. For chronic issues, test the well for iron bacteria or consider a chlorine injection system.

Why does water pressure stay low even after changing the filter?

Check the cartridge size—installing a 2.5″ diameter cartridge in a 4.5″ housing restricts flow and mimics a clog. Also verify the inlet valve is fully open and inspect the old cartridge; if it's clean, the pressure drop may be from sediment in the water heater or a partially closed valve elsewhere in the system.

This is educational information, not plumbing advice. If you see persistent leaks, cracked housings, or pressure issues after a filter change, call a licensed plumber to inspect the system.