Smell in water
Here is a suggestion as it won’t cure the issue. When living in Fallon the cold water would start to smell in all the sinks. We would change the water riser under all sinks, resulting in the smell being gone.
Never happened in the shower, just sinks.
Never found the cause, even asked the plumbers and no one had any suggestions besides live with it. So we changed out the riser as soon as the smell arrived.