An under-sink reverse osmosis system usually keeps a small storage tank that holds treated water until you open the dedicated faucet. The tank is what lets the faucet pour right away instead of waiting for the membrane to make new water. In a St. Louis kitchen, how you use that tank affects how often it refills, how the water tastes after a quiet stretch, and how fast you notice when something is off.
How the tank fills and empties
Treated water flows from the membrane into the tank, and the tank is kept under pressure by a small air charge on the side opposite the water. As you draw water, the pressure drops and the tank empties. When it is empty, the system makes water again until the tank is full. A system that seems slow to refill is not always broken. Low incoming supply pressure, a partly clogged pre-filter, or a long period without use can each slow the cycle.
Habits that change how the tank behaves
- Drawing a large amount at once, such as filling a pitcher for a gathering, empties the tank faster than normal use.
- Running the faucet for long periods to clear a sputter or flush the line uses stored water that the system then has to replace.
- Leaving the system idle for days or weeks lets the water sitting in the tank age, which can change the taste.
- Opening the faucet often in short bursts keeps the cycle busy and makes it harder to tell whether the tank is refilling normally.
Watching for a tank that is not right
Start by noting how the faucet behaves right after the tank should be full. A strong, steady flow for a short time, followed by a drop to a trickle, can point to low tank pressure or an air charge that has leaked down. Feel the tank itself. A tank that is properly pressurized and holds water will feel firm, while a tank that has lost its air charge tends to feel heavy and full all the time, even when the faucet is drawing water. Look at the tank and its fittings for drips or staining. Take care when you touch the fittings, because the system is connected to your supply line.
When to stop and call a professional
If the tank leaks, if the faucet sprays rather than flows, or if water collects under the sink after you close the faucet, shut off the feed valve to the system and stop using it until someone can look at it. Do not open the tank cap or valve fittings beyond what the manufacturer's manual describes. Keep the manual in a labeled folder with the date of your last service visit, and note the age of the tank if you can find it on the label. A local plumber familiar with under-sink filtration can check the tank pressure, the feed valve, and the drain line in one visit.
Keeping the tank useful through St. Louis seasons
St. Louis winters bring cold snaps that can chill under-sink plumbing, and summers can make kitchen cabinets warm and humid. If you notice condensation on the tank during the first warm days of spring, open the cabinet door a little to let air move. Avoid storing cleaning supplies or pet food directly against the tank, since a leak can ruin them and hide the leak. If you plan to be away for an extended stretch, run a short flush before you leave or shortly before you return, so the water in the tank is fresh when you use it. Ask a service person how long the system can sit before it should be flushed.