If you open the faucet on your reverse osmosis unit during a St. Louis winter and the water feels noticeably colder than it did in summer, you are not imagining it. The water you drink comes from a storage tank that sits in a cabinet, and that cabinet is affected by the same cold air as the rest of the house. This guide explains why that happens and what to check before you change anything.
Where the water in your faucet comes from
A reverse osmosis system does not make water on demand the way a tankless heater makes hot water. Incoming supply water passes through the filters and the membrane, and the purified water fills a small storage tank under the sink. When you open the RO faucet, that stored water flows out. The temperature you feel at the faucet is therefore largely the temperature of the water that has been sitting in the tank and lines, and that water takes on the temperature of the space around it.
In St. Louis, incoming supply water runs colder during the winter months than it does in warmer weather. A cabinet on an exterior wall, or one near a cold basement floor or crawlspace opening, can drop even further. A tank sitting in that space will feel cold to the touch, and the water inside will follow.
Check the cabinet first
Open the cabinet door and feel the tank, the lines, and the air around them. If the space feels close to the temperature of an unheated room, the cold is coming from the location, and you can usually see the cause. Look at these spots:
- An outside wall directly behind the sink, especially if the cabinet is pushed against it.
- Gaps around the plumbing where cold air can rise from a crawlspace or basement.
- A cabinet door that stays open during cold weather, letting room air in.
- A window or exterior door close enough to the sink to pull in drafts.
Tell cold water from stale water
Water that has sat in the tank and lines overnight can feel cool or flat even when the tank is not especially cold. Run the RO faucet briefly, then feel the water again. If the water feels noticeably different after the first draw, the issue is probably the water that sat overnight rather than a cold cabinet. If it stays cold through a longer draw, the cabinet is the more likely cause.
Look at the tubing and fittings
Small plastic tubing runs from the tank to the faucet and from the unit to the cold supply valve. Tubing that rests against a cold back panel, or that passes through a gap in the cabinet floor, can chill faster than you would expect. Check whether any line is pressed against the cabinet wall or lying on a cold surface. Do not bend or kink the tubing to make room, since that can restrict flow. Keep the lines loose and clear of surfaces that draw cold air into the cabinet.
Steps to try, in order
- Close the cabinet door fully, and check whether any gap around the pipes lets in cold air.
- Seal visible gaps with foam or a caulk made for plumbing penetrations, leaving room for the lines to move.
- Move any tubing away from cold exterior surfaces without kinking it.
- Run the faucet briefly before you fill a glass, so the freshest water reaches the glass.
- If the cabinet stays cold after sealing, note the location and ask a qualified plumber to look at the wall or crawlspace behind it.
When the cold is not the whole story
Cold water is not the only reason an RO faucet can feel off. If the water is cold and also slow to fill a glass, or if you hear new noises from the cabinet, the cause may be a restricted line, a low tank, or a filter that needs attention. Those are separate checks. Water that tastes or smells unusual is a different question as well, and it deserves its own look rather than being folded into a temperature check.
What to note for your St. Louis home
Keep a short note of the days you notice cold water, the weather on those days, and which cabinet you are checking. Over a St. Louis winter, a pattern often shows up, such as cold mornings after a cold night, or one corner of the house that runs colder than the rest. That pattern tells you where to spend your effort, whether that means sealing the cabinet, rerouting tubing, or accepting that a particular sink is cold and planning around it.