Changing RO Filters: How Often and How to Do It

Changing RO filters means replacing the pre-filters, post-filter and, less often, the membrane on a set schedule, usually every 6 to 12 months for the filters and every few years for the membrane on a typical tank system. The job itself is simple once you know which stage is which, what tools you need and how to check for leaks afterward. This guide covers both a typical 5-stage tank system and the Sanavia Hydra, which uses two tool-free cartridges.

What the filters in an RO system do

Most under-sink reverse osmosis systems stack several stages in a row. Each one protects the next, so a worn-out early stage can shorten the life of everything after it.

• Sediment filter. Catches sand, rust and grit before they clog the finer stages.
• Carbon filter. Adsorbs chlorine and many organic chemicals. Chlorine can damage RO membranes, so this stage matters.
• Carbon block filter. A denser carbon stage that catches what the first carbon stage missed, including more chlorine and chloramines.
• Reverse osmosis membrane. The heart of the system. Water is pushed through a very fine semi-permeable layer, and the dissolved solids it rejects go to the drain.
• Post-filter. A final polishing stage, usually carbon, that cleans up taste and odor before water reaches the faucet. On the Hydra, it also adds some minerals back.

The Sanavia Hydra runs water through the same five stages in the same order: sediment, carbon, carbon block, reverse osmosis membrane and post-filter. The difference is in how those stages are packaged for replacement, which we cover below.

How often to change RO filters

How often to change RO filters depends on the stage, your water and how much you use. Manufacturers set their own intervals, so your manual always wins. As a general guide, these are the typical ranges for a standard 5-stage tank system:

Stage	Typical replacement interval	What shortens it
1. Sediment filter	Every 6 to 12 months	Well water, old pipes, visible grit or rust
2. Carbon filter	Every 6 to 12 months	High chlorine or chloramine levels, heavy use
3. Carbon block filter	Every 6 to 12 months	Same as stage 2
4. RO membrane	Typically every 2 to 3 years, sometimes longer	Hard water, high TDS, skipped pre-filter changes
5. Post-filter	About every 12 months	Heavy use

Many owners change stages 1 through 3 together because it is easier to remember one date. Hard water, well water and water with a lot of sediment wear filters out faster, so lean toward the short end of each range if that describes your home. If you are not sure how hard your water is, a free water test gives you a TDS reading before you set a schedule.

The Hydra replacement schedule

The Hydra keeps things to one date on the calendar: replace both cartridges together every 12 months.

Cartridge	Replace every	Price
Sanavia Carbon Block Filter	12 months	$50
Sanavia 800G ROCB Filter (the high-capacity cartridge matched to the Hydra's 800 gallons per day output)	12 months	$100
Filter Bundle (both cartridges)	12 months	$125, $25 less than buying separately

Heavy use or sediment-heavy water can shorten that 12 months. Change both cartridges at the same time rather than staggering them.

Signs a filter is due

Even with a schedule, your water will usually tell you when a filter is worn out. Watch for:

• Slower flow. On a tank system, the tank takes longer to refill or runs out sooner. On a tankless system like the Hydra, noticeably slower flow at the faucet is the sign a cartridge is due.
• Taste or odor coming back. A chlorine taste, a flat or musty flavor, or a smell means the carbon stages are likely spent.
• Rising TDS. TDS (total dissolved solids) is the best quick check on how well the membrane stage is working. The Hydra shows TDS in real time, so a reading that creeps up over weeks is a clear signal. On other systems you can check with a handheld TDS meter. Read more in what TDS in water means.

Time and tools needed

On a typical housing-style under-sink system, a full filter change takes most people somewhere between half an hour and an hour, including flushing. You will usually need:

• The housing wrench that came with the system
• Replacement filters for each stage you are changing
• A towel and a small bucket or shallow pan for drips
• Food-grade silicone lubricant, if your manufacturer calls for it on the O-rings

The Hydra needs no tools for a cartridge change. Its cartridges twist and lock into place: you twist the spent one out and twist the new one in. There is nothing to unscrew and no wrench to hunt for. Keep a towel handy for any drips.

How to change RO filters

Here is how to change RO filters on a typical housing-style system with clear or opaque canisters that unscrew. Check your manual first, since steps and flush times vary by brand.

1. Shut off the feed water. Close the valve that feeds cold water to the RO system. On a tank system, also close the valve on top of the storage tank.
2. Relieve the pressure. Open the RO faucet and let it run until flow stops. This drains pressure from the lines so the housings will unscrew and will not spray.
3. Open the housings. Put the towel and pan underneath. Use the housing wrench to loosen each canister, then unscrew it by hand. Expect some water to spill.
4. Remove and replace the filters. Pull out each old filter and note its orientation. Rinse the empty housing with clean water. Many manufacturers also recommend sanitizing the housings during a filter change, so follow yours if it does. Unwrap each new filter and set it in place.
5. Check and lube the O-rings. Make sure each O-ring is seated in its groove, clean and not cracked. If the manufacturer calls for it, apply a thin coat of food-grade silicone lubricant.
6. Close the housings. Screw each canister back on by hand, then snug it with the wrench. Do not overtighten; that can crack housings or pinch O-rings.
7. Turn the water back on and check for leaks. Open the feed valve slowly, then the tank valve. Watch every housing and fitting for drips for several minutes, and check again a few hours later.
8. Flush per the manufacturer's instructions. New carbon filters release fine carbon dust, and new membranes need flushing before use. Many manufacturers have you fill and empty the tank one or more times. Follow the flush steps in your manual exactly.
9. Write down the date. A sticker on the housing or a phone reminder makes the next change easy.

How to replace RO filters on the Hydra

Replacing RO filters on the Hydra is a twist-out, twist-in job with no tools. Both cartridges are replaced together every 12 months, so the simplest option is the Filter Bundle.

1. Get both new cartridges ready. You need one Sanavia Carbon Block Filter and one Sanavia 800G ROCB Filter, or the bundle.
2. Prepare the area. Clear the cabinet and lay a towel under the unit.
3. Twist the spent cartridge out. Turn the first cartridge to unlock it and pull it free.
4. Twist the new cartridge in. Insert the new one into the standard Sanavia RO housing and twist until it locks.
5. Repeat for the second cartridge. Always replace both at the same time.
6. Check for leaks and run the faucet. Look at both cartridges for drips, then run water from the Hydra faucet.
7. Watch the TDS readout. The real-time TDS display gives you an easy baseline after the change. Note the number so you can spot a rise later.

That is the whole job. If you installed the Hydra yourself, the installation guide shows where everything sits under the sink.

RO membrane change

An RO membrane change on a typical tank system happens far less often than a filter change, usually every 2 to 3 years, and sometimes longer when the pre-filters are changed on time. The membrane is the most expensive part on most systems, and the pre-filters exist mainly to protect it. Skipping a sediment or carbon change is the fastest way to ruin a membrane early, because grit clogs it and chlorine breaks it down.

Signs of a worn membrane on a typical system include a TDS reading at the faucet that stays high even after new pre-filters, a tank that barely fills, and a return of the salty or flat taste the system used to remove.

RO membrane replacement steps (typical system)

1. Shut off the feed water and the tank valve, then open the RO faucet to relieve pressure.
2. Disconnect the tubing from the end cap of the membrane housing. Most systems use push-to-connect fittings: press in the collet and pull the tube out.
3. Unscrew the membrane housing cap. Pull the old membrane out with pliers if it is stuck.
4. Note the direction of flow and the O-rings on the membrane, then slide the new membrane in the same way, pressing firmly so it seats.
5. Replace the cap, reconnect the tubing and turn the water back on.
6. Check for leaks, then flush the new membrane exactly as the manufacturer directs before drinking the water.

On the Hydra, there is no separate membrane to change. The reverse osmosis membrane is built into the 800G ROCB cartridge, so replacing that cartridge every 12 months is the membrane change. With the carbon block cartridge alongside it, that is the whole maintenance schedule.

Common mistakes when changing RO filters

• Changing only one stage. A fresh post-filter will not fix a clogged sediment filter. Change the stages your manufacturer groups together, and on the Hydra change both cartridges.
• Skipping the flush. The first water through new carbon can look dark or cloudy. Fine carbon particles are harmless but not pleasant, so flush as directed.
• Overtightening housings. Hand-tight plus a small turn is usually enough.
• Using non-matching filters. Off-brand filters may not seal properly or may not match the system's flow rate. The Sanavia 800G ROCB Filter is sized for the Hydra's 800 gallons per day output.

Is the Hydra easier to maintain?

For most people, yes. The Hydra has five stages of filtration but only two cartridges to replace, both on the same 12-month schedule, with no tools. Because it is tankless, there is no storage tank to drain, sanitize or wait on. The real-time TDS readout takes the guesswork out of knowing whether the system is still performing. In independent lab testing of an Arlington, VA home's tap water, total trihalomethanes fell from 58 ppb to 2.79 ppb after the Hydra, a 95% drop. You can see the full lab results.

If you are shopping for a system, see the Sanavia Hydra. It is $999 to self-install or $1,250 professionally installed in the DC, Maryland and Virginia area, with free U.S. shipping, 60-day returns and a 3-year warranty.