How do I change a whole-house water filter?

Changing a whole-house filter cartridge is a short job once you know your housing: water off, pressure off, housing off, new cartridge in, then back the way it came. The two things that usually cause trouble are opening a housing that is still under pressure and a dry or twisted O-ring that leaks when the water comes back on. Models differ in the details, so keep your housing's manual at hand.

Before you start

Find how water gets shut off to the filter, and how the housing lets its pressure out.

• A head with a bypass. On GE's heavy-duty housing, for example, you turn the control handle on the filter head to BYPASS or OFF, then press the red pressure-release button on the head.^[1] In BYPASS, water keeps flowing to the house around the filter, so the release button is what empties the pressure from the housing.^[1]
• Shutoff valves or the main. Other systems have a shutoff valve on each side of the filter, or none, so you close the valves or the main shutoff. On Aquasana's whole-house system you then unscrew the pressure-relief valve on the sump cap, and with the main closed you can also drain the lines by opening a faucet inside the house; in bypass mode the lines do not need draining.^[2]

Have these ready:

• the replacement cartridge, matched to your housing's size and type
• the housing wrench that came with the system
• a bucket and a couple of towels
• food-grade silicone grease for the O-ring, and a spare O-ring if yours is old

Aquasana warns that its filter housings are heavy and will likely crack if dropped,^[2] so lower the housing with both hands.

Leave any copper wire clamped across the filter in place. GE warns: "A copper or galvanized cold water pipe may be used to ground electrical outlets in the home." GE adds that the filter housing may have broken this ground path, so where the pipe carries the electrical ground, the installer should have bridged the filter with a copper ground wire.^[1] Aquasana gives the same warning for copper pipes: leave the grounding clamps installed while you change the filter.^[2]

Cleaning, the O-ring and putting it back

With the old cartridge out, rinse the housing. Wash the inside of the housing with mild soap and water, not harsh cleaners or hot water.^[1]

The O-ring is what keeps the housing from leaking. Clean it, coat it lightly with food-grade silicone grease rather than petroleum jelly, and press it evenly into its groove.^[1][2] A flattened, cracked or stretched O-ring is often the cause of a drip after a filter change, so replace one that looks worn.

Set the new cartridge in the center of the housing, screw the housing on by hand, and snug it with the wrench. Both manuals say not to overtighten, and Aquasana notes the wrench should only need an eighth to a quarter of a turn.^[1][2]

Turn the water back on slowly, bleed the air with the release button, and look for drips. Then flush the cartridge before anyone drinks the water. GE's instructions are to flush the cartridge for 10 minutes (40 gallons), wait one hour, then flush again for 10 minutes before using the water.^[1] A carbon cartridge often sends out some black dust at first; that is what the flush is for.

How often to change it

Go by the schedule for your exact cartridge, not a general rule. GE's manual says to change the cartridge when the water flow is noticeably reduced or at least every 3 months, and its carbon cartridge is rated for 30,000 gallons or 3 months.^[1] Aquasana's whole-house iron filter cartridges are replaced every 6 months, sooner if the flow drops.^[2]

Overdue cartridges are not harmless. Virginia Cooperative Extension says activated carbon filters must be changed according to the manufacturer's recommendation to work properly,^[3] and Virginia Tech's well-water program warns that pitcher-style carbon filters that are not changed according to directions may actually become a source of contamination.^[4] There is more on schedules in how often to replace water filter cartridges.

Picking the right replacement

A sediment cartridge and a carbon cartridge can look alike and do different jobs. According to Virginia Cooperative Extension, sediment filters are rated by the smallest particle they can trap, such as 20 microns, and carbon filters treat taste, odor and chlorine.^[3] Buy the same type and rating unless you are deliberately changing what the filter does, and look for certification by an independent third party, like NSF International.^[3]

Know what a cartridge filter cannot do. GE's housing is meant for a potable, safe-to-drink cold water supply only, and in GE's words, "The filter cartridge will not purify water or make unsafe water safe to drink."^[1] If you are on a well and have not had the water tested, read how to know what water treatment system you need before buying anything more.

Stop and call a pro if

• The housing or head is cracked, or it still leaks after you have reseated a clean, greased O-ring.
• The leak is at the pipe fittings, not the housing. That is plumbing work on the supply line.
• There is no way to isolate the filter. Adding shutoff valves or a bypass means cutting into the supply line, and the Virginia Uniform Statewide Building Code requires a permit for installations or alterations involving the water supply and distribution system.^[5]
• The ground wire across the filter is missing or loose on copper or galvanized pipe. Have an electrician or plumber restore it.
• Your water pressure is high. GE's heavy-duty housing is rated up to 100 psi and calls for a pressure-reducing valve ahead of it if house pressure runs higher than 80 psi during the day.^[1]
• The housing is old. Aquasana says its housings must be replaced every 5 years.^[2] Check your own manual for the housing's service life.

Getting help in Virginia

Loclis lists DPOR-licensed plumbing businesses with their licence number and class. Look up plumbers in Blacksburg or another town, browse water treatment services, or find more plumbing answers.

If the flow is still weak after a fresh cartridge, describe the problem once and licensed local plumbers quote it.