How often should reverse osmosis filters be changed?

A reverse osmosis system needs very little maintenance, but not zero. If you let too much time pass between changes, water quality drops and the most expensive part, the membrane, wears out early. The good news: it's simple, cheap and schedulable. Here's exactly how often.

The filters and their schedule

A residential reverse osmosis system has five stages with different lifespans:

• Sediment and carbon (stages 1-3): changed once a year. They're the "pre-filters": they protect the membrane by removing sand, rust, chlorine and off-tastes.
• Osmosis membrane (stage 4): lasts 2-3 years depending on the water and use. In high-limescale areas like the Costa del Sol, it leans closer to 2 years than 3.
• Remineralizing postfilter (stage 5): changed together with the pre-filters, once a year.

What happens if I don't change the filters

The activated carbon pre-filter is the one that "protects" the membrane by removing chlorine. If it saturates and chlorine keeps getting through, the membrane degrades much faster: instead of 2-3 years, it can last under a year. And the membrane is the system's most expensive part.

Also, a saturated pre-filter means the water comes out with less flow and more off-tastes. It's the most common sign: "the tap takes longer and doesn't taste as good".

Signs it's time for a change (even before the year is up)

• Flow drops: filling a glass takes longer than usual.
• The chlorine taste returns: the carbon is spent.
• TDS rises: if you measure with a TDS meter and it goes past 50 ppm, the membrane is asking to be replaced.
• Odd noise or dripping from the unit: check it — not always the filters, but worth a look.

How we handle it for you

If we installed your system, we note the date and remind you ourselves when the change is due. We come, change the filters, check for leaks and verify water quality with a TDS reading. It's a fixed-price maintenance with no surprises and nothing for you to track.

Got a system from another brand that hasn't been checked in a while? We service it too: book a visit and we'll get it up to scratch.