Identify when the taste started. A change immediately after service points toward flushing or cartridge seating; a gradual change points more toward aging filters, stagnant storage or sanitation.
Taste changed right after a filter replacement
New carbon cartridges, membranes and remineralization stages often require a specified flush before drinking. Incomplete flushing can leave carbon fines, manufacturing residues or unusually strong mineral taste in the first batches.
Follow the exact manufacturer startup procedure rather than using a generic flush time for every system.
Aging post-carbon filters are a common taste culprit
The final carbon stage is designed largely for taste and odor polishing. Once it is exhausted or contaminated, finished-water taste can deteriorate even when membrane rejection still looks acceptable.
A filter can also be overdue before there is a dramatic change in faucet flow.
Stagnation and storage tanks matter
Water left unused in a tank or countertop reservoir can develop stale taste. Long vacations, warm storage conditions and overdue sanitation can make this more noticeable.
If taste improves after a full drain, refill and manufacturer-approved sanitizing procedure, storage conditions were likely part of the problem.
Do not use taste alone as a safety test
Taste cannot confirm whether a specific contaminant is present or absent. If the taste change is persistent, unusual, or accompanied by odor, visible particles or a known source-water issue, stop relying on taste as the diagnostic and use appropriate testing or service.