Reverse osmosis maintenance: filter, membrane and system service

Reverse Osmosis Company is an independent referral service, not an installer or plumber. When you send the form, your details go to an independent local water treatment pro who can contact you and prepare a quote.

What wears out in an RO system

The EPA’s WaterSense program describes reverse osmosis as pressure forcing water through a semi-permeable membrane, with treated water (permeate) going to the faucet and reject water (concentrate or brine) going down the drain. Around that membrane, a home system carries filters, each with its own place in line:

Part	Where it sits	What to follow
Sediment pre-filter	First in line, before the membrane	The maker’s change schedule
Carbon pre-filter or filters	Before the membrane	The maker’s change schedule
RO membrane	The heart of the system	The maker’s replacement schedule
Post filter	After the membrane, before the faucet	The maker’s change schedule
Seals and O-rings	In each housing	Inspected at each change

You will see change intervals quoted all over the internet, and they disagree, because systems and water differ. This site does not print one. The schedule that counts is the one in your system’s manual or on the maker’s site, and your pro can read it with you. A label inside the cabinet door with the date of each change makes the next one easy to time.

Why the schedule matters

The pre-filters sit ahead of the membrane, which is the part that does the reverse osmosis itself, and the post filter is the last stage before the faucet. Your system’s manual explains what each stage is there for and when it is due. Slower flow or a change in taste are worth mentioning to a pro, and the filter dates are one of the first things they may ask about.

There is also the reason you bought the system. The EPA says RO systems can potentially remove contaminants such as lead, volatile organic compounds, PFAS, arsenic, bacteria and viruses. If you bought the system for a particular contaminant, keeping to the maker’s schedule, with the parts the maker specifies, is part of using it the way it was certified.

What a reverse osmosis service visit covers

Ask the pro what their visit includes. A thorough reverse osmosis service can cover:

• Shutting off the supply and relieving the pressure before any housing is opened.
• Replacing the pre-filters, and the membrane and post filter when they are due.
• Cleaning the housings and checking each seal and O-ring.
• Sanitizing the system, where the maker calls for it, with the maker’s method.
• Checking the storage tank, on systems that have one.
• Checking fittings, tubing, the faucet and the drain connection for drips.
• Flushing the system as the maker’s instructions say before it is used again.
• Writing the date of the change on a label in the cabinet.

Reverse osmosis filter replacement: doing it yourself

Search for reverse osmosis filter replacement and page one is stores selling cartridges. Plenty of people change their own filters, and a system with easy twist-off cartridges is designed for it. If you do it yourself:

1. Buy the exact filters and membrane your system’s maker specifies, or ones certified for the same job.
2. Read the maker’s instructions all the way through first.
3. Shut off the water feeding the system and relieve the pressure as the maker describes.
4. Have a towel and a shallow tray ready: housings hold water.
5. Check every seal as you go, and seat it properly before closing a housing.
6. Flush the system as the maker says before drinking the water.
7. Check for drips over the next day.
8. Write the date on a label.

People call a pro when the housings are stuck, when a seal will not seat, when the membrane is due and its housing is awkward, when they are not sure which filters the system takes, or when they would just rather not. Each of those is a fair reason.

RO membrane replacement

The membrane does the actual reverse osmosis. Signs a membrane may be due include slower flow after the pre-filters have been changed, and treated water that tastes more like the tap. The maker’s schedule is the guide. When you replace it, use a membrane the maker specifies for your system, so the system keeps working the way it was certified to.

Signs that maintenance is overdue

• You do not know when the filters were last changed.
• The faucet runs slower than it used to.
• The water tastes or smells like plain tap water again.
• The drain seems to run longer than it did.
• There is a drip at a housing or a fitting.

Some of these overlap with repairs. If a filter change does not fix it, see reverse osmosis system repair.

On a well, or after the water changes

If your RO system is on a private well, keep testing the well. The EPA advises testing a private well every year for total coliform bacteria, nitrates, total dissolved solids and pH, and testing again after any part of the well is repaired or replaced. A change in the well’s water can change what the RO system is dealing with, so tell the pro. See reverse osmosis for well water.

Reverse osmosis service on an older system

Sometimes a service visit turns into a different conversation: the filters for an old system are hard to find, the housings are cracked, or the system sends a lot of water down the drain. The EPA says a typical point-of-use RO system generates five gallons or more of reject water for every gallon treated, some inefficient units up to 10, while a WaterSense labeled unit must send 2.3 gallons or less. If a pro suggests replacing the system, ask for the comparison in writing. See RO installation.

What to tell the pro

• The brand and model of the system, if you can see them on a housing or the faucet.
• When the filters and membrane were last changed, if you know.
• Any sign of trouble: slow flow, taste, a drip, a running drain.
• City water or a private well.
• Whether the system also feeds a refrigerator or ice maker.

Keeping a simple maintenance record

The easiest maintenance plan is a written one. Keep a note, on a label inside the cabinet door or on your phone, with four lines: the system’s brand and model, the date it was installed, the date of each filter change and the date of each membrane change. Add the part numbers of the filters it takes. When you ask a pro for a service visit, read them the note. It saves a trip to find out which filters to bring.

Keep the system’s manual with the note. The maker’s schedule, the flushing steps after a change and any sanitizing method are all in it, and they are what a careful service follows.

If the system feeds a refrigerator or ice maker

An RO system tied to a refrigerator’s water dispenser or ice maker has more tubing and more fittings than one that feeds a single faucet. Mention the extra line when you book a service, so the pro checks it too. Some refrigerators carry their own water filter as well. Ask whether the refrigerator’s filter is still needed with the RO system feeding it, and follow the refrigerator maker’s advice on that.

Questions to ask about a service visit

• Which filters and membrane will you fit, and are they the maker’s parts or certified for the same job?
• Will you sanitize the system, and with which method?
• Will you check the tank, the fittings, the faucet and the drain connection while you are there?
• What does the visit cost in writing, with and without the membrane?
• Do you keep a record of what you changed and when?

Send the form with your ZIP code and choose ‘Filter and membrane change’. Your request goes to an independent RO pro who works in your area. Asking is free, and you never have to buy. If you have no system yet, start with RO installation or how reverse osmosis works.

Questions people ask