A white or grey crust on a kettle, a cloudy film on a showerhead, and spots that dry on glass all point toward hard water. A brown or orange stain in a sink, a toilet bowl, or a tub can look similar at a glance, but it usually comes from iron, and a standard softener does not fix iron the way it fixes hardness. Telling the two apart saves you from buying the wrong fix.
Look at the stain first
Hardness deposits tend to be chalky, white, grey, or slightly crusty. They build up on surfaces that get hot, such as the inside of a kettle, the heating element of a coffee maker, or the bottom of a water heater you can access. They also cause soap to lather poorly and leave dishes and glass with a spotty finish.
Iron stains are usually rust-colored, orange, or brown, and they often appear as streaks or rings in a sink or bowl. Water with iron can also taste metallic, and it can leave yellow or brown marks on white laundry. Dark grey or black specks can point to manganese, which is a separate issue again.
Check where the problem shows up
Look at whether the stain is on the hot side only, the cold side only, or both. Heavy scale on the hot side and not the cold side suggests hardness is building up in heated appliances. Staining that appears on both sides, or that shows up right after the water sits in a pipe or tank, is more likely to be iron or another dissolved metal.
Get the right test
A water report is the only reliable way to separate these causes. Ask for a test that lists hardness and iron (and manganese, if you see black specks) as separate results. A basic hardness reading alone will not tell you whether iron is present. Your water utility may publish a report, or a certified lab can test a sample for you.
What to ask a seller before you buy
Once you have the numbers, ask the seller directly whether the unit is rated for the iron level in your report and whether it needs a pre-treatment step. Ask what the manufacturer or installer recommends if iron is present and whether that adds parts or ongoing service. Compare the answers in writing. If the seller cannot tell you how the unit handles iron, treat that as a reason to pause.
If you want to see how different units are scored on criteria like this, the ratings page lists the current comparison, and the methodology page explains what each score is based on.