Fix
Fixing a Water Softener Smell
A water softener smell usually starts in the brine tank, where bacteria grow in stagnant brine, or in the well water itself. Sniff the brine tank and compare softened and unsoftened taps to find which, then clean and sanitize.
Quick answer
- Smell only at the brine tank points to bacteria in stagnant brine.
- Smell at unsoftened taps too means the source water, not the softener.
- Clean the brine tank, then sanitize the resin with unscented bleach.
- Rotten-egg well water needs a sulfur filter ahead of the softener.
- Never pour vinegar into the brine tank.
Where the smell comes from
Odor around a softener has two main sources. One is the softener itself. According to Pentair's 5600SXT manual, organics and bacteria arriving with the supply can build up inside a softener and leave the water tasting or smelling off. The other is the water coming into the house, such as hydrogen sulfide in well water, which smells like rotten eggs whether or not a softener is installed.
A quick check tells them apart.
- Smell the brine tank. Lift the lid. A sour, swampy or rotten-egg smell from the salt and water inside points to the brine tank.
- Compare taps. Run a cold tap that bypasses the softener, such as an outside spigot (often left on hard water), and a cold softened tap. If both smell, the source water carries the odor. If only the softened tap smells, the softener is adding it.
- Compare hot and cold. Odor only on the hot side points toward the water heater, a separate problem worth having a plumber look at.
- Put the softener in bypass for a day. If the smell at the softened taps fades, the softener is the source.
Brine tank smells
SoftPro's guide to brine tank odor says a rotten-egg smell from the tank comes from sulfur-reducing bacteria growing in stagnant water. Long-standing brine, a tank not emptied in years and mushy salt sludge all give bacteria a place to settle.
Several habits keep the tank fresh:
- Keep it covered. A lid that stays on is one of Pentair's basic brine tank rules.
- Use clean salt. SoftPro recommends evaporated salt for an odor-prone tank. Both the Fleck and Pentair manuals rule out rock salt, which carries dirt into the tank. The pellets vs crystals guide compares the clean options.
- Clean on a schedule. Look inside at least once a year and clean when sludge or dirt builds up. SoftPro's odor guide suggests cleaning every 6 to 12 months where smells recur; Pentair's manual suggests about every three years for a tank in good condition.
- Watch for mushing. A soft, muddy salt layer under the brine is a sign the tank needs emptying and scrubbing; see the brine tank cleaning guide.
Rotten egg water
If unsoftened taps smell as bad as softened ones, the softener didn't create the odor. Rotten-egg water from a well usually means hydrogen sulfide, and a salt-based softener isn't built to remove it. Hydrogen sulfide, iron bacteria and oxidized iron need a dedicated iron or sulfur filter installed ahead of the softener. Pentair's manual and SoftPro's install guide both place filters for iron and odor upstream, so the softener is the last treatment step, with only a UV system after it in SoftPro's layout.
A softener can still pick up a smell from sulfur water, because the same bacteria and organics that come in with the supply can foul the resin and brine tank. Sanitizing helps, but the smell will return until the source is treated.
| What you notice | Likely source | First fix |
|---|---|---|
| Rotten egg smell at the brine tank only | Sulfur-reducing bacteria in stagnant brine | Clean the tank, then sanitize |
| Musty smell at softened taps only | Organic or bacterial fouling of the resin | Sanitize the softener |
| Rotten egg smell at every tap | Hydrogen sulfide in the well | Sulfur filter ahead of the softener |
| Chlorine smell after a cleaning | Bleach still in the lines | Flush cold taps until it clears |
Clearing it
Work from the brine tank to the resin, then flush the house lines. Before starting, switch to bypass and pull the valve's plug.
- Empty and clean the brine tank. Quality Water Treatment's cleaning guide covers the steps: disconnect the lines, drain the brine away from plants, remove the old salt, wash the walls with a soft brush and mild soap, then let a solution of a quarter cup of bleach per 2 to 3 gallons stand for 15 minutes, scrub once more and rinse until clean.
- Refill the tank. Reassemble it, add fresh water (Quality Water Treatment says at least 5 gallons after cleaning) and clean salt.
- Sanitize the resin. Pour unscented household bleach into the brine well, never the resin tank. Dose by resin volume and follow your manual: Pentair lists 1.2 fl oz per cubic foot, while SoftPro and Quality Water Treatment use about 2 fl oz per cubic foot. Then run a manual regeneration; SoftPro allows at least an hour of contact time and adds an extra rinse. The full method is in how to sanitize a water softener.
- Flush the plumbing. SoftPro says to run a cold tap about 20 minutes, until the chlorine smell is gone.
- Retest. SoftPro suggests checking again 5 to 7 days later.
Skip the vinegar. Both stores warn against adding it to the brine tank, and Quality Water Treatment reserves a weak vinegar soak for small parts taken off the valve.
If the smell comes back within weeks, look again at the source water, and work through the troubleshooting guide and the maintenance checklist for anything left open.
Related guides
Common questions
Why does the softener room smell like rotten eggs after the unit sat unused?
Water left standing in the brine tank is where SoftPro says sulfur-reducing bacteria grow. A long stretch without regeneration, such as a vacation in bypass, gives them time. Clean the tank and sanitize before putting the softener back in normal use.
Does a smell mean the resin is ruined?
Not by itself. Pentair's manual treats odor from organic or bacterial fouling as something to disinfect away. If smell and hardness both return quickly after sanitizing, the resin may be badly fouled and worth replacing.
Is a bleach smell normal after sanitizing a softener?
Yes, for a short time. SoftPro says to run a cold tap about 20 minutes, until the chlorine smell clears, before using the water normally.
Can potassium chloride stop a brine tank from smelling?
Switching salt type won't remove bacteria already in the tank. The fix is cleaning and sanitizing, then keeping the tank covered and stocked with clean pellets or crystals.
More help: see our water softener how-to guides.