When to Replace Water Filtration

Water Filtration  · 

Overdue cartridges and what loading actually does

A cartridge gives up slowly. Carbon adsorbs contaminants until the available sites are occupied, and once they are, the media stops reducing them; some compounds can also desorb back into the water as conditions change, which is why a long-neglected carbon filter can leave water tasting worse than the untreated supply. Sediment cartridges load from the outside in, so the pressure drop climbs and flow at the tap weakens while the cartridge is still passing water. Reverse osmosis membranes compact and foul, so production falls and rejection drifts.

The reliable signals are falling flow, a change in taste or odour, and time in service. Where the system has a meter, gallons treated is the better measure, and the interval should be whichever of volume or time arrives first. Writing the installation date on the housing costs nothing and removes the guesswork.

Worn housing threads, sumps and o-rings

Every time a housing is opened, the o-ring is compressed, reseated and exposed to whatever grit sits on the rim. Eventually it flattens, hardens or tears, and the leak appears at the joint rather than in the cartridge. Cross-threaded sumps are the other common failure: forcing a sump onto damaged threads cuts new ones and the housing never seals properly again.

Inspect the threads and the o-ring groove at every change. A gritty groove needs wiping, a dry ring needs food-grade silicone lubricant, and a ring that is cracked or deformed needs replacing before the sump goes back on. If the threads are chewed, the housing is finished, because housings are not repairable and a weeping sump is a water damage risk rather than a nuisance.

Reading reverse osmosis membrane decline

A membrane declines gradually and then noticeably. Production rate falls, the storage tank takes longer to refill, and the water may begin to taste different as rejection of dissolved solids weakens. A growing pressure loss across the system, an increase in the volume of water sent to drain, or a change in the taste of the permeate all point to a membrane that is fouling, scaling or has been damaged by chlorine.

Compare the permeate against the feed with a total dissolved solids meter to see how much the membrane is still rejecting; a narrowing difference means there is little left. Before replacing it, check the pre-filters, because a loaded carbon stage that has stopped removing chlorine will damage the next membrane exactly as it damaged this one.

Pressure tanks that have lost precharge

A reverse osmosis storage tank holds water because a bladder separates it from a charge of compressed air. When that precharge bleeds away, the tank behaves as if it were much smaller: drawdown falls, the pump or supply has to work harder, and the system may short-cycle as the tank refills a little and empties again immediately.

Check the precharge at the air valve with the tank empty of water and the system depressurised, then compare the reading with the pressure the maker specifies, which is normally set somewhat below the system’s cut-in pressure. A tank that will not hold a charge has a failed bladder and needs replacing, because topping up the air will not keep air and water separated for long.

Discontinued cartridges and freeze-damaged housings

A cartridge that has been discontinued signals that the system is nearing the end of its supported life. Sellers run down stock, and what remains on offer is usually a generic lookalike whose performance is not the same as the original. Holding a small stock of genuine cartridges buys time, but eventually the housing itself becomes the constraint, and the choice falls between a substitute cartridge of unknown provenance and a new system.

Freeze damage is more immediate. Water expands as it freezes, and a housing or membrane vessel left in an unheated building over winter can crack along a seam or at a fitting boss without any obvious external sign. Inspect any unit that has been through a hard freeze before returning it to service, and treat hairline cracks, weeping joints or a bulging sump as a replacement rather than a repair.

When replacing the unit beats replacing parts

The arithmetic becomes clear once you list everything that needs attention. Add cartridges, o-rings, the membrane and the storage tank, then add any housings with damaged threads or freeze cracks, and compare the total against a current system with supportable replacement parts. If the list includes both a membrane and a pressure tank, the parts usually cost more than a comparable new set.

Other reasons to replace rather than repair are a change in what you need removed, such as a system built for taste that now has to handle a contaminant it was never specified for, and a configuration that cannot be extended, such as a housing with no room for a sediment pre-filter. A system whose consumables are still available, whose housings are sound and whose job has not changed is worth maintaining; one that fails several of those tests is not.

FAQ

How often should a carbon cartridge be changed?

Follow whichever comes first: the rated volume for your water quality, or the maker’s time limit. Carbon can exhaust on time alone through compounds adsorbed from water sitting in the housing, so a cartridge in a lightly used system still needs changing on schedule.

Can a cartridge be cleaned and reused?

A sediment cartridge is sometimes rinsed, but rinsing does not restore capacity and the media stays loaded. Carbon blocks and membrane elements cannot be restored at all. Reusing an exhausted cartridge gets you the pressure drop without the reduction.

My reverse osmosis tank fills slowly and empties quickly. What is at fault?

Those two symptoms together usually mean the tank precharge is low or the bladder has failed, and the membrane may also be producing slowly. Check precharge with the tank empty, then measure production rate, and decide whether the tank, the membrane or both need replacing.

Is it worth replacing a housing with damaged threads?

No. Housings are not repairable, and a sump that will not seal properly leaks under pressure. Replace the housing or the whole unit, and check whether the same damage affects the other housings in the set.