Yellow water almost always comes from one of three things: dissolved iron, manganese, or organic tannins leached from decaying vegetation. Which one you have decides the fix, and you can narrow it down in an afternoon with a clean glass, a note of which taps are affected, and whether the color clears when the water stands.
Run the simple tests before buying anything
Fill a clear glass from the cold tap and let it stand. If the color settles to a rusty deposit at the bottom, that is oxidized iron already out of solution. If the water is clear at the tap and turns yellow or brown as it sits, the iron is dissolved and oxidizing in the glass. If the color is uniform, does not settle and looks like weak tea, suspect tannins. Note whether hot taps only are affected, which points at the water heater.
Iron and manganese: the common answer
Iron and manganese are naturally present in many groundwater supplies and carry secondary standards, which are aesthetic rather than health based. Penn State Extension gives recommended maximums of 0.3 mg/L for iron and 0.05 mg/L for manganese, above which staining and discoloration become obvious. Manganese tends toward brown black rather than orange. A test that reports both, and reports total versus dissolved, is what tells you which treatment will hold.
Tannins, and why filters disappoint
Tannins are dissolved organics from peat, leaf litter and shallow groundwater. They give a yellow tea tint that will not settle out, resists sediment filtration entirely, and passes straight through an iron filter because there is nothing to oxidize. The treatment is a tannin selective anion resin, or in mild cases carbon, and it needs its own regeneration regime. Fitting an iron filter to a tannin problem is money spent on the wrong machine.
When it is the plumbing, not the supply
If only the hot taps run yellow, look at the water heater: a corroding tank or an exhausted anode rod discolors hot water while the cold stays clear. If every tap suddenly runs yellow on a municipal supply, call the utility, because hydrant flushing and main breaks stir settled iron into the distribution system and it clears by itself. Sudden discoloration on a well after heavy rain suggests surface water reaching the casing.
Questions people ask about water yellow
Is yellow tap water dangerous to drink?
Iron and manganese discoloration is an aesthetic issue rather than a health standard, but yellow water on a well warrants a test before you assume it is harmless.
Will a water softener clear yellow water?
Only sometimes. A softener can hold modest amounts of dissolved iron, but oxidized iron fouls the resin, and it does nothing at all for tannins.
Why is only my hot water yellow?
That points to the water heater rather than the supply: a corroding tank or spent anode rod discolors hot water while every cold tap stays clear.
The water cleared on its own. Do I still need treatment?
If it was a one off after main flushing, no. If it returns whenever demand rises or after rain, the source is yours and a test is the next step.