Water Filtration Maintenance Checklist

Water Filtration  · 

Interval math: gallons first, months second

Every cartridge has a rated volume in gallons and often a maximum time in service, and the correct interval is whichever limit arrives first. A carbon block held wet past its time is not improving with age; it becomes a surface for bacterial growth and can begin releasing what it adsorbed. Write the install date on the housing with a marker so nobody has to reconstruct it from memory.

The rated volume assumes a stated influent. Water with heavy chlorine demand consumes carbon capacity faster than the label suggests. Chloramine is worse than free chlorine because the carbon has to break the chlorine-ammonia bond, and it needs catalytic carbon to do it, so intervals tighten again. Iron and manganese in well water load the pre-filter long before its gallons are used. Hard water scales a reverse osmosis membrane and shortens its life in a way that has nothing to do with the rating printed on the element.

Practically, that means reading your own water and adjusting downward rather than trusting the box. A household that cooks and drinks heavily, or runs a heavily chlorinated municipal supply, should treat the printed gallons as an upper bound, keep one spare cartridge on the shelf, and watch for the taste change that signals breakthrough.

O-rings: food-grade silicone, not petroleum grease

The o-ring is the only thing sealing a screw-on sump, and it is where most leaks and most cartridge bypass start. Petroleum-based grease attacks EPDM and natural rubber, causing them to swell and take a set, which is why the tube in a service kit is food-grade silicone. Apply a thin film with a fingertip, not a blob, and keep it out of the thread path where it collects grit.

Replace any ring that is flattened, cracked, nicked or visibly compressed, and check the groove in the sump for sediment that stops the ring seating. A dry ring grabs on assembly and can roll out of its groove, which looks like a leak from the threads and gets misdiagnosed as a cracked housing. Rings are consumables: keep several of the correct size with the spare cartridges, because a generic ring of the wrong thickness will either leak or never let the sump seat.

When you reassemble, hand-tighten the sump and then use the supplied wrench for a final quarter turn. Greasing the ring is what makes the sump turn smoothly; over-torquing is what cracks shoulders and chews threads.

Sanitising a reverse osmosis system

A reverse osmosis system has a chlorine-free, wet, dark downstream side, which is exactly the environment bacteria like. If the system sat unused for weeks, if the water develops an odour, or if you are recommissioning a stored unit, sanitising is worth the hour.

Never sanitise the membrane or the carbon stages with chlorine: a thin-film composite membrane is destroyed by it, and carbon will strip the sanitiser while holding some of it. Remove those elements first. Depressurise the system, drain the tank, then wash the housings and lines with warm water and a mild detergent and apply a chlorine-based sanitiser intended for potable water systems, following the dilution and contact time on its own label rather than guessing. Flush thoroughly, then fit fresh pre-filter, post-filter and membrane.

The post-carbon polishing stage absorbs chlorine, so it is the one element that must be replaced after any sanitising, not reused. Flush several tank volumes until no chlorine smell or taste remains before drinking the water, and reset the cartridge meter so the next interval starts from a known point.

Sediment pre-filters do the visible work

The first stage exists so the expensive stages do not have to. Spun-bonded polypropylene is a depth filter with a graded structure that traps particles throughout its thickness; pleated filters are surface filters that hold less but can be rinsed a few times. Both are rated in microns, and the pre-filter should be coarser than the carbon block behind it, so it takes the bulk load and the block handles adsorption.

A clear sump makes the decision easy, because you can see the colour creep from the outside in. Letting a pre-filter load too far raises the pressure drop across the whole system, starves the carbon block of contact time and can let captured material slough off downstream. On well water or old galvanised pipe, expect to change this stage far more often than the carbon block, and buy a small stock rather than a single element.

Rinsing a pleated element buys one short extension at most. Rinsing a spun-bonded depth filter does not restore it: the captured particles sit throughout the matrix, and the visible surface clean is not the same as a clean filter.

Membrane signals: TDS creep, slow production, rising concentrate

A membrane tells you it is failing in three ways, and all three are measurable. Product water drifts upward in total dissolved solids when measured against the feed, tank fill times lengthen so a glass or two empties the tank, and the ratio of concentrate going to the drain rises relative to permeate. A salty or flat taste usually arrives after the numbers have already moved.

Measure with a TDS meter on both feed and product, and account for temperature before diagnosing anything. Cold feedwater is less permeable, so production falls and product TDS rises in winter without any membrane fault. Then rule out the cheap causes in order: a loaded pre-filter, a tank that has lost its air charge, a failed automatic shutoff valve, or a clogged flow restrictor. Membranes are often replaced when the tank was the problem.

When the membrane is genuinely spent, replace the pre-filters at the same time. A new element behind a loaded pre-filter and a contaminated post-filter will not deliver clean water for long. Never let a membrane dry out and never expose it to chlorine, both of which cause irreversible damage rather than a recoverable decline.

Pressure tank precharge and waterlogged tanks

A reverse osmosis storage tank is a bladder inside a steel shell. The shell holds air, the bladder holds water, and the air charge is what pushes water out at the faucet. Check the charge when the tank is empty of water: isolate the tank or open the faucet until flow stops, then read the Schrader valve with a tyre gauge.

If water comes out of the valve, the bladder has failed and the tank is scrap, because the air side is now water. If the gauge reads low, add air with a bicycle or foot pump to the setting the manufacturer specifies. Too little charge and the tank fills nearly solid, which delivers a trickle at the tap and shuts off the system early; too much and the tank stores very little water and clicks on and off quickly.

Checking precharge takes five minutes and prevents the most common misdiagnosis in water filtration: buying a membrane when the real fault is an air charge that has leaked away over a couple of years. Recheck it whenever production slows, before touching the membrane.

Cleaning housings, threads and heads

Before opening any sump, relieve pressure with the housing’s release button or by closing the feed and opening the faucet. Then use the wrench made for the sump flats. A strap wrench on a smooth polypropylene sump can distort and crack it, and a cracked sump fails under pressure rather than at a convenient moment.

Clean the inside with warm water and a soft brush. Abrasive pads scratch the surface where sediment then clings, and solvent-based cleaners attack the plastic. Rinse until the water runs clear, and pay attention to the o-ring groove and the shoulder where the ring seats. Inspect the threads on both sump and head for cross-threading, burrs and the fine hairline cracks that run from the thread roots, then check the head’s sealing face and any bypass plunger for scale and grit.

A cross-threaded sump is the result of starting it by hand at an angle, so always thread it on by hand until it seats before the wrench goes anywhere near it. If a sump will not seal with a new ring and clean threads, replace the sump rather than adding tape to the threads, which does nothing on this style of joint.

Storing spare cartridges

Activated carbon adsorbs from the air as readily as from water, so a cartridge left open in a garage full of paint, fuel and exhaust is quietly loading up on solvents before it is ever fitted. Keep spares in their sealed bags, in a dry cupboard away from sunlight and heat, and off a cold concrete floor.

Observe a service life for inventory too. Rotate stock first in first out, write the purchase date on each bag, and check that the o-rings and any washers are in the box before you need them. Do not freeze carbon blocks; a block that has taken up moisture and then frozen can crack. Reverse osmosis membranes ship wet in a preservative, so store them sealed, upright and above freezing, and leave them wrapped until the moment of installation.

A cartridge that has already been wet in a housing and then left to sit for months should be replaced rather than dried and reused. It has been through a growth period, and drying does not undo it. Label each spare with the model number it fits so a system change does not leave you with a shelf of parts that no longer fit anything.

FAQ

How often should I change a carbon block on heavily chlorinated water?

Sooner than the printed rating. Carbon capacity is consumed by the chlorine demand of the water passing through it, so a heavy residual or chloramine shortens the useful life of the block. Watch for taste and odour breakthrough, and treat the rated gallons as an upper bound rather than a promise.

Can I clean and reuse a sediment filter?

A pleated surface filter can be rinsed once or twice as a stopgap. A spun-bonded depth filter cannot be restored, because the trapped particles sit through its thickness rather than on the surface. Given how cheap this stage is, replacing it is usually the better call.

Why does my reverse osmosis water taste odd after sanitising?

Residual sanitiser is being picked up from the housings, lines and tank. Flush several tank volumes with the post-filter fitted and discard the water, and if the taste persists, replace the post-carbon stage, since it holds chlorine and releases it slowly.

Do I need a TDS meter to know when the membrane has failed?

It is the most useful tool you can own for a reverse osmosis system. Comparing feed and product readings spots rejection loss before you taste it. Remember that cold feedwater lowers production and raises product readings, so judge the trend over weeks rather than a single reading.

Is it safe to store spare cartridges in a garage?

Not if the garage holds solvents, fuel, paint or a running engine. Carbon adsorbs airborne chemicals, and freezing can crack a damp block. Keep spares sealed in a dry, heated cupboard, and rotate them first in first out so nothing sits for years.