Beyond the Cartridge: The Complete Guide to Water Filtration System Parts That Need Replacement
By Jared Beviano, Owner of Water Wizards Filtration | January 2025
Everyone knows you need to change water filter cartridges. That's the obvious part — the sediment filter turns brown, you swap it out. The carbon block gets exhausted, in goes a new one. But here's what twelve years of servicing filtration systems across South Florida has taught me: cartridges are maybe 40% of the maintenance story. The other 60%? All the parts nobody thinks about until something goes wrong.
Last month I got a call from a frustrated homeowner in Jupiter. His iSpring whole house system was leaking at the housing, even though he'd just changed the filter himself. Drove out there expecting to find a cracked housing or cross-threaded cap. Instead? A $2 O-ring that had gone flat and brittle after three years of use. He'd been changing cartridges religiously every six months but never once thought about the rubber seal that makes the whole thing work.
This guide covers everything that wears out, degrades, or eventually fails in water treatment systems — all the parts beyond the obvious filters and membranes. Some of these you can replace yourself. Some require a professional. All of them matter more than most people realize.
The Seal Problem: O-Rings and Gaskets
If there's one category of parts that causes more service calls than any other, it's seals. Every filter housing, every pressure vessel, every connection point in your water treatment system relies on rubber or silicone seals to prevent leaks. And rubber doesn't last forever.
How O-rings fail in Florida. Our combination of heat, humidity, chlorine exposure, and minerals creates perfect conditions for seal degradation. The O-ring on a filter housing might last five years in Minnesota. Down here? I tell customers to inspect them every two years and plan on replacement every three to four years, even if they look okay. The rubber gets hard, loses elasticity, develops flat spots from constant compression. You don't see a crack — you just notice water seeping from the housing one day.
The most common O-ring failures I see involve whole house filter housings — the Pentek Big Blue series, iSpring WGB housings, Express Water, and Culligan standard housings all use similar O-ring sizes. The housing cap screws down onto the sump, compressing that ring to create a watertight seal. Every time you open the housing to change a filter, you stress that O-ring. Open it dry, without lubricant, and you're grinding rubber against plastic. Do that twenty times over a few years and the seal starts to fail.
The silicone lubricant rule. Every filter change should include inspecting the O-ring, cleaning off any debris or grit, and applying food-grade silicone lubricant before reinstalling. Dow Corning Molykote 111 is the industry standard — NSF certified, won't degrade rubber or plastic, and makes housing removal much easier next time. Never use petroleum jelly or WD-40. Petroleum products break down rubber and can contaminate your water. I keep tubes of Molykote 111 on the truck and use it on every service call.
RO system O-rings multiply the problem. A typical under-sink reverse osmosis system like the iSpring RCC7 or APEC ROES-50 has at least seven O-rings: one on each of the three pre-filter housings, one or two on the membrane housing (both ends on some models), one on the post-filter housing, and various seals in the quick-connect fittings. The iSpring ORF kit, for example, includes replacement O-rings for the entire RCC7 series. I recommend replacing all RO system O-rings every 2-3 years or whenever you notice any housing starting to weep.
Whole house systems scale up accordingly. The SpringWell CF1 has O-rings on the sediment pre-filter housing. The Aquasana EQ-1000 has multiple seal points. Pelican systems, KIND Water, US Water Systems — they all rely on gaskets and O-rings throughout. Tank-based systems like water softeners have O-rings at the control valve connection, at bypass valves, and internally within the valve mechanism itself.
Filter Housings: When the Shell Cracks
Filter housings are designed to last years, but they're not indestructible. I replace housings on maybe one out of every fifty service calls — not common, but when it happens, you need to act fast.
Pressure-related failures. Big Blue and Slim Line housings are rated for specific pressure ranges, typically 80-100 PSI maximum. Florida well systems with variable pressure pumps can spike above that during pressure tank cycling. Over time, these pressure fluctuations fatigue the plastic. I've seen housings that looked perfect suddenly develop hairline cracks after years of pressure cycling. The first sign is usually a slow seep at the housing sump — not from the O-ring but from an actual crack in the plastic.
UV degradation. Clear and blue housings installed in sunlight or areas with UV exposure can become brittle over time. The polypropylene degrades, turns yellowish or hazy, and eventually fails. If your whole house system is installed in a location with any sun exposure, opaque housings last longer than transparent ones.
Chemical attack. Heavily chlorinated water, water with unusual pH, or water that's been treated with oxidizers can degrade certain plastics over time. I've seen housings from iSpring, Pentek, and others that became cloudy and soft after years of exposure to aggressive water chemistry.
When to replace. Visible cracks or crazing are obvious replacement triggers. But also watch for housings that become difficult to seal even with new O-rings, housings that feel soft or flexible compared to when new, and any housing that's been over-tightened to the point of thread damage. A new housing is typically $25-75 depending on size and quality. Compared to water damage from a failed housing, that's cheap insurance.
RO System Components: The Parts Inside the Cabinet
Reverse osmosis systems have more replaceable parts than any other residential water treatment equipment. Beyond filters and membranes, here's what wears out:
Storage tank bladders. The pressurized storage tank on traditional RO systems contains a rubber bladder that separates stored water from an air charge. Over time — typically 5-8 years — this bladder can lose integrity. Symptoms include the tank feeling heavy when full (waterlogged, no longer holding air pressure), slow delivery of water even with a full tank, or water that tastes stale because it's sitting in a compromised bladder. You can test tank pressure with a bicycle pump and tire gauge at the Schrader valve on the bottom of the tank. Should read 5-8 PSI when the tank is empty. If you can't hold pressure, the bladder is shot.
Tank replacement vs. repair. You can't replace just the bladder — if it fails, you replace the entire tank. Fortunately, standard 3.2 or 4-gallon tanks are reasonably priced ($50-80) and use standard 1/4" or 3/8" connections. The tank valve itself (the fitting on top that connects to tubing) can also fail — typically an O-ring issue that can be rebuilt for $10-15 versus $50+ for a new tank.
Check valves. Every RO system has at least one check valve to prevent backflow. When check valves fail, the system may run continuously, waste water, or allow contaminated water to flow backward through the system. The symptom I see most often: the system runs and runs, never shutting off, because the check valve isn't holding pressure. These are $5-15 parts that can be replaced in minutes.
Auto shut-off valves (ASO). The ASO is what tells your RO system to stop producing water when the tank is full. When ASO valves fail — typically after 4-7 years — the system either runs constantly (valve stuck open) or produces no water (valve stuck closed). The Aquatec and Pentek ASO valves are industry standards, around $20-40 to replace.
Flow restrictors. That little plastic piece in the drain line controls how much water goes to waste versus how much becomes product water. Flow restrictors are sized to match your membrane's production capacity. A clogged or incorrectly sized restrictor causes poor system performance. These are $3-8 parts that occasionally need cleaning or replacement.
Faucets. RO faucets have moving parts — specifically the air-gap mechanism (on air-gap models) and the dispensing valve itself. After years of daily use, faucet handles can become stiff, air gaps can clog, and seals can fail. A slow drip from a closed faucet is usually a worn internal seal. Faucet replacements run $30-100 depending on finish and style. The Tomlinson Pro-Flo is my go-to for durability.
Tubing and fittings. The 1/4" polyethylene tubing that connects RO components can become brittle, kinked, or develop pinhole leaks over time. John Guest-style quick-connect fittings are mostly reliable, but the internal collets that grip tubing can wear out after many disconnections. If a fitting won't hold tubing securely anymore, replace it — $2-5 per fitting.
Booster pumps. Some RO systems (especially the Waterdrop tankless units and some well water installations) include booster pumps to increase feed pressure. Pump motors typically last 5-10 years. The Aquatec permeate pump, which uses waste water pressure rather than electricity, can last longer but still has diaphragms and check valves that eventually need attention.
Water Softener Components: More Than Just Resin
Water softeners are mechanical systems with dozens of individual parts. Resin replacement gets all the attention, but here's what else wears out:
Control valve internals. Whether you have a Fleck 5600SXT, a Clack WS1, or a proprietary valve from Kinetico, Culligan, or EcoWater, the valve contains seals, spacers, pistons, and O-rings that wear over time. The Fleck 5600 rebuild kit (part #60125 seals and spacers, #60102 piston, #60032 brine valve) is something I stock on the truck because these components fail regularly after 8-12 years of service.
Symptoms of valve wear include: hard water breakthrough even when the softener appears to be regenerating, excessive water in the brine tank, failure to draw brine during regeneration, water leaking from the valve body, and regeneration cycles that don't complete properly.
Brine valve and injector assembly. The brine valve controls the flow of salt water into the resin tank during regeneration. The injector creates the suction that draws brine from the salt tank. Both can become clogged with sediment or salt deposits, and both have O-rings and seals that degrade. When a softener "stops drawing brine," it's usually an injector screen that needs cleaning or a brine valve that needs replacement. Parts cost $20-50; labor to access and replace them takes 30-60 minutes.
Timer motors and circuit boards. Electronic softener heads (like the Fleck SXT series) have timer motors that drive the regeneration cycle and circuit boards that control everything. These are 10-15 year components in most cases, but power surges can kill them prematurely. Replacement timer motors run $40-80; circuit boards $80-150 depending on the model.
Riser tubes (distributor tubes). Inside every softener and backwashing filter tank is a vertical tube that runs from the control valve to the bottom of the tank. At the bottom is a screen or basket that prevents resin from escaping up the tube during service or down the drain during backwash. Riser tubes rarely fail, but the bottom screens can crack or clog. If you're finding resin beads in your water or at faucet aerators, suspect a broken distributor screen. This requires emptying the tank to repair — a 2-3 hour job.
Brine tank components. The salt tank contains a safety float (to prevent overflow), a brine well (the tube that draws brine), and a grid plate (the platform at the bottom that keeps salt above the water level). Salt bridges, where a crust forms over the salt pile leaving an air gap, are usually a maintenance issue rather than a parts issue — but I've replaced grid plates that dissolved in aggressive water and brine wells that cracked from age.
Bypass valves. The bypass allows you to route water around the softener during regeneration or maintenance. Bypass valve O-rings and seals wear out, causing the valve to leak or allowing hard water to bypass during normal operation. Most bypass rebuilds are $15-30 in parts.
Whole House Tank Systems: Media and More
Tank-based whole house filters — SpringWell CF1, Pelican PC1000, Aquasana Rhino, US Water Systems, and similar — have their own replacement needs beyond the obvious media:
Media tanks (mineral tanks). The FRP (fiberglass-reinforced plastic) tanks used in most residential systems are incredibly durable, but not immortal. I've seen tanks fail after 15-20 years, usually at the neck where the control valve threads in. Symptoms include slow leaks at the valve connection that can't be fixed by replacing O-rings, visible crazing or cracking in the tank shell, or complete structural failure (rare but dramatic when it happens).
Tank replacement is major surgery. You're removing the control valve, draining and disposing of the old media, physically replacing the tank, installing a new riser tube, adding gravel (if required), loading new media, and reinstalling everything. Count on $200-400 for the tank itself plus several hours of labor plus new media costs.
Upper baskets and screens. Some tank systems use an upper basket or screen that attaches to the control valve head and prevents media from being drawn into the valve during service. These can crack or clog over time. The RKIN and similar systems make upper basket replacement fairly straightforward — 30 minutes to remove the head, swap the basket, and reassemble.
Control valves. Just like softeners, backwashing filter systems use control valves with internal parts that wear. Fleck and Clack valves dominate the aftermarket filter space. Budget $50-150 for rebuild kits, more if you need to replace the entire valve head.
UV System Components: Beyond the Lamp
UV sterilization systems seem simple — water flows past a lamp, organisms die — but there's more to maintain than annual lamp replacement:
Quartz sleeves. The quartz sleeve is the clear tube that separates the UV lamp from the water. It allows UV light to pass through while protecting the lamp from water contact. Quartz sleeves should be inspected annually and replaced every 2-3 years, or immediately if cracked. The sleeve can develop scale deposits from hard water, mineral films from iron, or biofilm from bacterial contamination — all of which reduce UV transmission. I clean sleeves at every lamp change and note their condition. A new Viqua VH200 sleeve is around $65-85; Sterilight sleeves run $45-65.
Ballast units. The ballast is the electronic component that powers the UV lamp. Ballasts typically last 8-15 years but can fail earlier, especially in hot, humid locations (like most Florida utility areas). When a ballast fails, the lamp won't light or won't maintain proper output. Replacement ballasts run $100-200 depending on the system.
O-rings and end caps. UV systems have O-rings at each end of the chamber that seal around the quartz sleeve. These degrade over time, especially if the sleeve has been removed multiple times. End cap O-ring kits are $10-20 and should be replaced whenever you replace the quartz sleeve.
UV sensors. Higher-end UV systems (Viqua D4, E4, Trojan UVMax premium models) include UV intensity sensors that monitor actual output. Sensors can drift over calibration or fail after 5-10 years. A failed sensor might trigger false alarms or, worse, fail to alert you when actual output drops. Sensor replacement is $50-150 depending on the system.
Plumbing Components: The Infrastructure
Water treatment systems don't exist in isolation — they connect to your home's plumbing through various components that also wear out:
Inlet and outlet fittings. Threaded connections at the filter housing or valve head can develop leaks over time. The threads themselves don't usually fail, but the Teflon tape or pipe dope sealing them can dry out and shrink. Re-wrapping threaded connections during system maintenance is cheap insurance.
Flexible connectors. The braided stainless steel lines connecting systems to household plumbing have a finite life — typically 8-12 years. The rubber inner hose degrades, the braiding can corrode if moisture penetrates, and the crimp fittings can fail. I recommend replacing flex connectors proactively rather than waiting for leaks.
Pressure relief buttons. Most Big Blue housings have a red pressure relief button that releases system pressure before you open the housing. These occasionally stick or fail to seal properly. Replacement buttons are model-specific and usually available from the housing manufacturer.
Drain saddle valves. RO systems typically connect to the drain via a saddle valve that clamps around the drain pipe. These can clog with debris, leak at the clamp seal, or develop internal blockages. Replacement is straightforward but occasionally reveals a bigger problem — like a drain line that's been gradually clogging for years.
Feed water valves. The angle stop or saddle valve that supplies water to your treatment system can fail like any other valve. Self-piercing saddle valves (common for RO installations) are particularly prone to problems — the pierced hole can clog with debris, and the valve itself tends to seize after years without operation.
How to Track What's Been Replaced
After reading all this, you might be wondering how anyone keeps track of it all. Here's the system I recommend to customers:
Keep a maintenance log. Physical notebook, phone notes, whatever works for you. Record every filter change, every service call, every part replaced. Include dates, part numbers, and any observations about system condition.
When we install a system, I include a laminated card with the installation date, filter types and sizes, recommended replacement intervals, and a QR code linking to our online portal where customers can track their maintenance history and order parts.
For DIY maintainers, set calendar reminders. Six months out for filter checks, annually for UV lamps, two years for O-ring inspections, three years for comprehensive system evaluation.
When to Call a Professional
Some of this work is genuinely DIY-friendly. Changing filter cartridges, replacing O-rings on accessible housings, swapping UV lamps — most handy homeowners can handle these tasks.
Other work requires experience, specialized tools, or just someone who's done it before. Softener valve rebuilds involve precise reassembly of multiple components. Tank media replacement requires knowing how to funnel media without clogging the riser tube. UV ballast replacement might require electrical knowledge depending on your installation.
My general rule: if you're unsure, call. A service call to have someone watch while you do it yourself (and catch any mistakes) is cheaper than fixing the water damage from a botched repair.
The Bottom Line: Systems Need Complete Care
Your water filtration system is exactly that — a system. Filters are the most obvious consumable, but O-rings, seals, valves, sensors, tanks, and plumbing components all contribute to system function. Neglect any of them and you're not getting the water quality you're paying for.
At Water Wizards, we inspect all accessible components during service calls, not just the parts we came to replace. We note O-ring condition, housing integrity, tank pressure, valve operation, and anything else that might become a problem. Because catching a $2 O-ring before it fails is always better than emergency service for a flooded utility room.
Questions about your system's maintenance needs? Not sure what parts are due for replacement? Call us at 561-352-9989. We service every brand mentioned in this guide and plenty more.
Keep those systems healthy, South Florida.
About the Author
Jared Beviano is the owner of Water Wizards Filtration, serving Palm Beach County and South Florida since 2013. Licensed water treatment specialist with certifications in residential and commercial filtration systems.
