Most under-sink reverse osmosis filter cartridges carry a printed date or code somewhere on the label. That marking tells you when the cartridge was made or when it should be replaced. Homeowners in St. Louis often find the sticker only after a filter has been in place longer than they expected. Knowing where to look and how to read it makes scheduling changes much simpler.
Where to Look
- The cardboard box the cartridge came in, usually on an end flap or side panel.
- The label printed directly on the cartridge body, often near the top or along the side.
- The filter housing itself, where some setups have a tag or a handwritten note from the installer.
- Your own records, such as a receipt, an order confirmation, or a note in a household binder.
How to Read a Code
Codes differ by manufacturer, so the safest step is to check the instruction sheet for your specific model. Many labels show a month and year, which is straightforward to read. Others use a short string of letters and numbers that needs the instruction sheet to decode. If you cannot find any date at all, treat the cartridge as unknown rather than fresh.
Set Your Own Calendar
Once you know the manufacturing or purchase date, count forward using the replacement interval printed in the instructions. Put a reminder on your phone for the replacement month, and write down the date you actually installed the cartridge. The install date matters because a cartridge can sit on a shelf for a while before it goes into a housing.
Check Every Stage
Under-sink systems usually have several filters in sequence, and each one may have its own code. Walk through each stage and record what you find. Note whether each cartridge is a sediment stage, a carbon stage, or a membrane, since replacement timing can differ from one stage to the next.
If the Date Is Missing or Worn
- Photograph the label before you remove the cartridge so you keep a record.
- Check the instruction sheet and saved receipts for the model and purchase timing.
- If the label is faded, look for the model number on the housing or box and use it to find replacement guidance.
- If the cartridge is unreadable and you have no record, plan to replace it on your normal schedule rather than stretching it out.
Taste and Flow Are Not Date Checks
Some homeowners treat a change in taste or slower flow as a sign that a filter is spent. Those changes can come from many causes, including other stages, the faucet, or the water supply itself. A date is a more dependable starting point than guessing from how the water seems. If you want to know what is actually in your water, that is a separate question, and a certified lab can help you decide what to test for.
When to Ask for Help
If you cannot identify the cartridges or the housing has no readable markings, a local water professional in the St. Louis area can help you match parts. Your water utility's customer service line can also answer general questions about your supply. Bring your list of what you found so the conversation moves faster.
Keep a Simple Log
- The stage name and where it sits under the sink.
- The printed code or date, with a photo.
- The install date and the date of the next change.
- The model number and where you bought it.
A short log taped inside the cabinet door keeps this information where you need it. It also helps anyone who services your St. Louis home know what is installed without digging through boxes.