Water rising through a bathtub drain usually means a shared drain line is partly or fully blocked and water is finding the lowest available opening. If it happens when a toilet flushes or a washing machine drains, the problem is probably beyond the tub itself.
Connect the backup to the fixture that was being used
Note whether water rises when a toilet flushes, a sink empties, or a washing machine pumps out. That relationship helps identify which fixtures share the restricted drain line.
A bathtub is a common low point for backups
The bathtub drain opening is often lower than other fixtures, so it may show a main-line problem first. Cleaning hair from the tub drain will not solve water arriving from another branch.
Reduce water use in the affected area
Every discharge adds volume behind the restriction and can make the backup overflow. Avoid showers, washing machines, and connected toilets until the level falls and the blockage is located.
Wastewater backup needs proper cleanup and service
If the water contains waste, paper, or a strong sewer odor, avoid direct contact and keep children and pets away. A shared or main drain blockage often requires professional plumbing equipment and access.