This is the question people ask right before they decide, and it's usually standing in for a different one: what does this actually commit you to?

Fair concern. Unlike a garrafón, which tells you it's empty by being empty, a water filter is one of the few things you buy that quietly stops working without ever mentioning it. So here's the real schedule, what a service visit involves, and what happens if you ignore it.

How often water filter cartridges need changing

Across every drinking water system we install in Mexico City, the rhythm is the same:

  • Sediment and carbon block: every 6 months. These do the bulk work: catching rust and grit from old building pipes, and pulling out chlorine.
  • Granular carbon and post-filter: every 12 months. The second carbon stage and the final polishing filter run on a yearly cycle.
  • Ultrafiltration membrane: every 12 months. Evans specifies annual replacement on the cartridge itself.
  • Reverse osmosis membrane: every 24 months. RO membranes genuinely last longer, and Purikor rates theirs at 24–36 months. We replace at 24 rather than stretching it, because CDMX water is harder on a membrane than the average the rating assumes. But we're not going to swap a part yearly that the manufacturer says lasts two to three years.
  • UV lamp: every 12 months, on the 6-Stage RO + UV system only. UV lamps dim long before they burn out, which is why they're replaced on a clock rather than when they fail.

The showerhead filter and the kitchen faucet mount follow that same 6-month rhythm. The bathroom sink filter is the one exception on our whole menu, and it runs on two clocks: the cartridge is swapped monthly (a small filter doing a small job, so it loads up faster), and you do those yourself from the six we leave at install. Then every six months we replace the entire faucet unit and restock your cartridges, so that one is always a new device rather than an aging one.

Our maintenance plans show the cost per system as a monthly figure, billed every six months alongside the actual visit. You're never charged before we've confirmed a time with you.

What happens on a maintenance visit

It's a short visit, and it's the same sequence every time:

  1. Shut off the water and depressurize the system.
  2. Swap whichever cartridges are due.
  3. Sanitize the housings and the lines while the system is open.
  4. Flush the new media through until the water runs clear.
  5. Check every fitting and connection for leaks.
  6. Confirm flow and taste at the faucet before we leave.

Step three is the one worth knowing about. Our other articles are honest that in a properly maintained system, the remaining risk sits in the tubing and storage rather than the membrane. Sanitizing at every visit is the step that addresses exactly that, and it's the reason a service visit isn't simply a cartridge swap you're paying someone else to do.

What goes wrong when you skip it

There are two failure modes, and only one of them announces itself.

The part you'll notice. Flow drops first. A sediment cartridge loading up with rust and grit restricts water before it does anything else, so the tap gets slower and slower over weeks. Then taste comes back: as the activated carbon exhausts, chlorine starts breaking through, and the water tastes like it did before you had a filter.

The part you won't. Both of those are late symptoms. The protective failure happens earlier and silently, and this is the part we'd rather you heard before you needed it.

Activated carbon isn't designed to remove bacteria: it removes chlorine, which is the thing that was suppressing bacterial growth in the first place. Research on point-of-use carbon block filters found that once a cartridge had processed about 85% of its rated volume, bacterial counts in the water leaving the filter plateaued at up to 100 times the counts going in. Replacing the cartridge brought those counts back down.

Two honest qualifications on that. First, it's a finding about carbon filters specifically, and in our multi-stage systems the carbon sits upstream of the ultrafiltration or reverse osmosis membrane, so an overdue carbon cartridge is still backstopped, provided the membrane itself is current. Second, it means the opposite of what people assume: the cheapest carbon-only products, like a faucet mount or a bathroom sink filter, are the ones where an overdue cartridge matters most, because nothing downstream is catching what grows on it.

Either way, the lesson is the same. “It still tastes fine” is not evidence that a filter is still protecting you. That's the entire reason these run on a schedule instead of on your judgment.

Can you change the cartridges yourself?

Technically, yes. There's no proprietary lock on any of it, and we're not going to pretend there is.

Three things make it go wrong in practice, and they're worth weighing honestly:

  • Remembering is the actual hard part. This is the one that gets people, and it isn't about competence: it's that nothing reminds you. A cartridge doesn't beep. Six months is long enough that a task with no deadline and no symptom simply doesn't surface, and by the time something does surface you're already in the silent-failure window described above. We track every system we install on a schedule in our own system and reach out when yours is due, which is most of what you're actually paying for.
  • Buying the wrong part. Local marketplaces are full of cartridges with the right dimensions and the wrong specification. Here's the one that catches people: carbon blocks all come in the same 2.5″ × 10″ size, but in different micron ratings, and the finer ones cost noticeably more. The Evans systems we install take a 1-micron block; the Purikor systems take 5-micron. Both drop into either housing and look identical sitting in the cabinet. Put a 5-micron block in an Evans and you've quietly removed the only fine filtration standing in front of the membrane — and nothing about the water afterward will tell you.
  • Damaging the system. Housings need the right torque: under-tighten and it weeps, over-tighten and you deform the O-ring and it weeps anyway. Cross-thread a housing or nick a membrane seating it and you've turned a cartridge change into a replacement. A slow leak inside a cabinet in an older CDMX apartment is an expensive way to save a service fee.

There's also the sanitize step, which most people swapping their own cartridges skip, understandably, since it's the part that doesn't feel necessary.

The bathroom sink filter is the honest exception, and it's genuinely a different situation: a clip-on cartridge with nothing to torque and no plumbing to disturb. That one is designed for you to change, which is why we hand you six at install rather than coming back twelve times a year to do something that takes you seconds. The unit itself we still replace outright every six months, on the same visit as everything else.

Why maintenance matters more in a Mexico City apartment

Cartridge life is rated on the assumption of reasonably clean incoming water. That's not what most buildings here deliver.

Tap water reaching your kitchen has come through aging municipal mains, then your building's own plumbing, then a rooftop tinaco that may or may not have been cleaned in the last year. Every bit of sediment that picks up along the way lands in your first-stage cartridge. In the older Roma Norte and Condesa buildings we work in most, that first stage does noticeably more work than the manufacturer's schedule assumes.

Which is also why the single highest-value thing you can do for your own cartridge life costs you nothing from us: get the tinaco cleaned about twice a year. We don't do that work and we're not selling it. It just means everything downstream lasts longer.

The short version

Sediment and carbon block twice a year, the rest annually, and the reverse osmosis membrane every two years, with a short visit each time that includes sanitizing rather than just swapping. Skip it and you'll notice the flow and the taste eventually — but the protection lapses well before either of those tells you anything. On CDMX tap water, with the sediment load most buildings here add, that schedule is the floor rather than a cushion.

If you'd rather not track any of it, that's what the maintenance plan is for. If you'd rather handle it yourself, ask us and we'll tell you which cartridge your system takes.

Sources

  • Effect of Point-of-Use Activated Carbon Filters on the Bacterial Quality of Drinking Water — on heterotrophic plate counts rising in filter effluent as cartridges approach their rated volume, and falling again after replacement.
  • “The microbial colonization of activated carbon block point-of-use filters,” Environmental Science: Water Research & Technology, 2017.
  • “Challenges of point-of-use devices in purifying tap water: the growth of biofilm on filters,” Science of the Total Environment.