A smell is data. Before buying anything, work out whether it comes from the water, from your plumbing, or from the drain, because all three smell like the tap to a person standing at the sink. Four checks separate them: hot against cold, one tap against another, a glass carried to another room, and inside against an outside spigot.
Four checks that cost nothing
First, run hot and cold separately. A smell on hot only points at the water heater. Second, compare the kitchen with a bathroom and an outside spigot: a single-fixture smell is that fixture's problem. Third, fill a glass, walk into another room and smell it there. If the glass smells fine away from the sink, you were smelling the drain, not the water. Fourth, if the smell appears on every tap, hot and cold, it is coming in from the supply and treatment is the answer.
What each smell usually means
Rotten egg is hydrogen sulfide. On hot water only, it usually comes from a reaction between the water heater's magnesium anode rod and sulfur compounds in the supply, and swapping to a different anode material often resolves it. On both hot and cold it is sulfur in the source, common on wells. Chlorine or pool smell is disinfectant residual. Musty or earthy usually follows a seasonal algae bloom upstream. Fishy or oily smells more often come from the drain trap than the water.
Check what your utility already published
On a city supply, much of this is documented. Every community water system publishes an annual Consumer Confidence Report and the EPA maintains a finder for locating yours. It names the disinfectant in use, which settles whether you are smelling chlorine or chloramine, and lists what was detected in the year covered. Utilities also run temporary chlorine conversions in some seasons, which is a frequent cause of a smell that appears for a few weeks and then goes.
Treating a smell that really is in the water
Chlorine odour responds to activated carbon at the kitchen tap or on the whole house. Chloramine needs catalytic carbon and a longer contact time, so a small cartridge will underperform. Sulfur on a well is treated by oxidation and then filtration, sized on a lab result. Smells that are actually coming from the drain or the aerator need cleaning, not equipment, and nothing you plumb into the line will make any difference to them.
Questions people ask about tap water smells
Why does my tap water smell like rotten eggs?
Hydrogen sulfide. On hot water only, the water heater anode rod is the usual cause. On hot and cold together, the sulfur is in the supply.
Is smelly water unsafe to drink?
Most odours are aesthetic rather than hazardous, but a sudden new smell is worth reporting to your utility or testing if you are on a well.
Why does the smell go away after running the tap?
That points at water that has been sitting in your own plumbing rather than at the incoming supply, often in a rarely used branch line.