White residue on faucets is usually mineral scale, especially calcium and magnesium left behind as water droplets evaporate. It is a clue that the water is hard, not proof that the water is unsafe.
Look for the evaporation pattern
Scale often forms around the aerator, faucet base, or places where droplets sit. If the residue feels soapy or greasy, cleaner or soap buildup may be involved instead.
Check for other hard-water clues
Spots on shower glass, faster scale buildup in water-heating equipment, and soap that rinses poorly all support the hard-water explanation. Water hardness can be tested if you need a number.
Clean without damaging the finish
A cloth dampened with white vinegar can dissolve deposits on many finishes, but it is not suitable for every stone, metal, or coating. Check manufacturer care instructions first.
If it returns quickly, think prevention
Drying the faucet after use reduces visible deposits. A water softener makes sense only when hardness causes enough problems to justify the maintenance, salt, and water use.