Not enough information. Type of water system? Copper/plastic/Galvanized steel. Maybe get the water tested to see if it is properly chlorinated.

Thanks for your replys, and apologies for insufficient info. I will try to paint the whole picture here: My water comes from a water district in the San Diego area (Rincon del Diablo Municipal Water District) My plumbing is all copper - 20 yrs old. I have a Nevien NPE-240A tankless water heater that is 2 years old. I have a Fleck 5600XT Water Softener - 1 year old. The 1st attachment shows the disinfection byproducts, residuals, and precursors resulting from the water treatment process The 2nd attachment shows the contaminants in my water. Rincon stated there is no iron in the water.

The yellow color in the water is caused by of a high concentration of iron and manganese. ... Some of the water color may be iron bacteria that thrive on the iron found in your pipes. The iron bacteria are harmless, but they cause yellow stains and can hold-up your water system.