A new under-sink reverse osmosis system needs a flush before anyone drinks from it. During manufacturing and shipping, small amounts of carbon dust, packing material, and assembly residue can end up in the filters and tubing. A careful flush clears most of that out, so the first water from your faucet in a St. Louis kitchen comes from a system that has been run the way it was designed to run.

Start With the Instructions in the Box

Each model has its own flush sequence. Some call for a rinse step on each cartridge, while others flush only through the membrane and storage tank. Read the included guide before you open any valves, and follow its order exactly. If the paperwork is missing, look up the model number printed on the unit and find the manufacturer's documents online. Write down any step you do not understand and get an answer before you start.

Set Up Before You Begin

  • Keep the RO faucet closed at the start.
  • Confirm the cold feed valve to the system is open.
  • Place a bucket or large pot under the drain point and keep it ready.
  • Clear the cabinet so you can see the filter housings, tubing, and storage tank connection.
  • Lay down a towel, since the early part of the flush can splash.

A Typical Flush Sequence

Your manual may differ, but many systems follow a pattern like this.

  1. Open the RO faucet and let water run into the bucket until the flow slows to a thin stream. This pushes air out of the storage tank.
  2. Close the faucet and let the storage tank refill fully.
  3. Open the faucet again and drain the tank as completely as the manual describes.
  4. Repeat the fill and drain cycle as many times as the instructions call for, then let the system refill one last time.
  5. Run the faucet until the water flows steadily and looks clear before you use it for anything.

What You Should See During the Flush

Expect the water to look cloudy at first. That usually clears as the system runs. Fine black specks in the first water often come from carbon fines in a new filter, and they should stop appearing as you keep flushing. If the water stays cloudy, has a strong or unusual smell, or the drain flow stays very weak even after the steps are finished, stop and check the troubleshooting section of the manual before going further.

Testing After the Flush

A flush removes residue, but it does not tell you what is in your water. If you want to know how the system is performing, a sample sent to a state-certified laboratory gives a clearer answer than a simple color strip. If you can, collect a sample of untreated St. Louis tap water first, then one from the RO faucet after the flush. Comparing the two results shows you what the system is doing. Keep the reports with your system paperwork.

Record Your Dates

Write the install date and the date you finished flushing on the filter housing or in a paper file near the unit. These dates help you plan future cartridge changes and make it easier to answer questions if something changes later. Many homes around St. Louis have different plumbing ages and layouts, so a clear record is useful no matter who works on the system later.

When to Stop and Get Help

If the flush does not go as the manual describes, pause and get help before using the water. If a professional installed the system, contact the person or company that did the work first. If you installed it yourself, review the troubleshooting section and the manufacturer's support contact information. Until your questions are answered, use a different source of drinking water so you are not relying on a system you are unsure about.