Soak a clean cloth in white vinegar. Wring out the cloth so that it is wet but is not dripping.
Rub the cloth over the water marks until they are gone. If the mineral residue doesn’t go away immediately, lay the cloth on the minerals for 10 minutes. Then, remove the cloth.
Dip a toothbrush into white vinegar, and scrub it over the hard water marks on the furniture if you can still see the marks.
Rinse the furniture with clear water, and dry it immediately with a clean cloth.