The answer to 'water softener foul smell' is that a foul odor coming from your water softener is usually caused by bacterial growth or a buildup of mineral deposits. This can happen when the softener isn't maintained properly or if it's been sitting unused for a while.
Some common symptoms include a rotten egg or sewage-like smell coming from your taps or appliances. This is often caused by sulfate-reducing bacteria that thrive in the moist environment of the softener. Mineral buildup can also trap debris and create an ideal breeding ground for bacteria. Regular maintenance and cleaning the softener can usually resolve the issue, but in some cases, you may need to replace the resin beads or other components.