Sanitizing a reverse osmosis system means circulating a disinfectant through the housings, tank and lines while the membrane is removed, then flushing everything thoroughly before the system goes back into service. It is a job worth doing at cartridge changes, after the system has stood unused, and any time the stored water starts to smell.
When sanitizing is actually called for
Do it at the annual filter change, after a house has been empty for weeks, after any plumbing work that opened the cold supply, and whenever water from the RO faucet develops a musty or eggy smell that a fresh carbon cartridge does not clear. A system that runs daily and gets its cartridges changed on schedule rarely needs more. Sanitizing is maintenance, not a rescue for a supply with a live bacteria problem.
The sequence, in order
Shut the feed valve and the tank valve, then open the RO faucet and drain the tank completely. Unscrew the housings, discard the used cartridges and take the membrane out of its vessel and set it aside, because chlorine based sanitizer destroys thin film membranes. Wash the housings and tank port, add the disinfectant the system maker specifies to the first housing, reassemble empty, then open the feed and let the tank fill so the solution reaches every surface.
Contact, flush, and back into service
Leave the solution standing in the tank and lines for the dwell time the manufacturer states, then drain the tank fully through the faucet. Refill and drain it again, and repeat until there is no smell or taste of disinfectant at the faucet. Only then refit the membrane and fit fresh cartridges, and drain one more tankful to purge carbon fines. Skipping the flush is the mistake that produces a chemical taste for weeks afterward.
What sanitizing does not fix
If the incoming water is the source of the contamination, cleaning the appliance changes nothing: it will recolonize within days. A well that tests positive for bacteria needs disinfection at the source and a treatment train that keeps it out, which our well water testing guide walks through. Likewise a rotten egg smell that is present at every tap in the house is a supply problem, not a storage tank problem.
Questions people ask about how to sanitize reverse osmosis system
How often should an RO system be sanitized?
Once a year at the filter change suits most households, plus any time the system has stood unused or the stored water starts to smell.
Do I leave the membrane in during sanitizing?
No. Remove it first. Chlorine based sanitizers damage thin film composite membranes permanently, and a damaged membrane stops rejecting contaminants.
Can I use household bleach?
Only if the system maker states it and the dose they give. Follow their instruction rather than guessing, and flush until no taste or odor remains.
Why does the water taste odd after sanitizing?
The system was not flushed enough. Drain and refill the tank repeatedly until the taste is gone, and change the postfilter if it persists.