Water stains on wood floors range from white finish bloom to dark boards that wicked moisture. Dry the source first; repairs fail if water is still moving.
Stop the moisture
Fix leaks, dry wet underlayment if accessible, and run airflow. Do not refinish over damp wood.
White surface stains
Often finish-only. After the floor is dry, light abrasion and a recoat, or careful iron-and-cloth technique on small spots, can clear bloom. Test methods in a closet or corner.
Dark board stains
Sand the stained boards to clean fiber. Bleach only when tannin stains remain, then restain to neighboring boards and apply floor finish coats.
Cupped or swollen boards
If edges are high or joints tight from swelling, wait for full dry-down before sanding flat. Replacing badly cupped boards can be cleaner than forcing a sand.
For more repairs like this, start in the Water Damage & Stains hub. If you are working through a related problem next, see Water Damaged Wood Floor Repair (Easy DIY Restoration Steps) or Wood Floors from Dog Urine: Deep Cleaning and Restoration.
