If the water from your reverse osmosis faucet smells musty, earthy, or like rotten eggs, the odor is pointing to one of a few places: the water coming into the house, the hot water heater, the storage tank, or a filter or fitting in the under-sink setup. In St. Louis homes, the cause is often easier to find than it seems if you check things in a set order. Start with the simplest checks and move toward the parts that need a closer look.
Start by Comparing the Taps
Before you touch any parts, fill a clean glass from three places in the same kitchen: the cold tap at the sink, the hot tap at the sink, and the reverse osmosis faucet. Smell each sample right away, then smell it again after the water sits for a few minutes. Write down which ones have the odor. The results usually narrow the search quickly.
- If the cold tap smells and the reverse osmosis water does not, the odor is coming in with the supply, and the unit is doing its job on it.
- If only the hot tap smells, the water heater is the first suspect. Sulfur-type odors in hot water are often tied to bacteria that can grow in a water heater tank, especially when the tank sits unused for long periods.
- If the reverse osmosis water smells and the cold tap does not, look at the storage tank, the filters, and the faucet line.
Check the Storage Tank
A storage tank that holds treated water for long stretches can develop an odor if it sits too long between uses. Draw enough water from the reverse osmosis faucet to empty most of the tank, then smell the next batch. If the smell clears up after the tank refills and you draw water again, the old water in the tank was the likely source. Many homeowners who go on trips or leave the house quiet for a while notice this pattern.
Also check the tank for any visible film or residue at the fitting where the line connects. Do not open the tank or make adjustments unless the instructions for your unit say you can do so safely at home.
Look at the Filters
Carbon filters are the most common filter source of odor in a reverse osmosis setup. An old carbon filter can stop holding contaminants well and may release a smell over time. A new carbon filter can also carry fine dust and a faint odor until it has been flushed. Read the instructions that came with your filter, and follow the flushing steps before the first use. Write down the date each filter was installed, so you know whether a change is due.
If a filter was stored dry for a long time or left in a damp basement area, consider changing it even if the schedule has not come up yet. Storage conditions can affect how a filter performs, and a filter that smells bad should be replaced.
Separate Room Air From Water Smell
Some odors seem to come from the faucet when they are really coming from the room. A dry drain trap, a bathroom or basement drain with little water in it, or a vent problem can send sewer-type smells into the kitchen or basement air. To test this, fill a clean glass with water from the faucet, cover it, and smell the glass after a minute. If the water smells clean when covered but the room smells strong, the source is in the air, not the water.
What to Test Next
If the smell stays after these checks, you can ask a certified lab to run a water test for the substances you suspect. Describe the smell and the places you checked so the lab can suggest the right test. Hydrogen sulfide is a gas that gives water a rotten egg smell, and bacteria or certain minerals can cause musty or earthy notes. A lab report can tell you what is actually in the water, which a smell test cannot.
Also ask the water provider that serves your St. Louis address whether they have recent water quality information for your area. Their reports cover the supply coming into the house, so they can help you tell whether the problem starts before the water reaches your home or after it arrives.
When to Bring in a Pro
If the smell is strong, if it appears in several taps at once, or if the hot water and cold water both smell in ways that do not clear up with flushing, it is time to have a licensed plumber or water treatment technician look at the whole system. Bring your notes on which taps smelled, when the smell started, and when you last changed each filter. That record will help them find the cause faster and avoid guesswork.