When water backs up into a sink, the drain downstream cannot carry water away as fast as it arrives. The cause may be a local blockage, a shared dishwasher or appliance connection, or a deeper drain restriction if other fixtures react too.
Notice what event triggers the backup
Notice whether the backup happens when the sink drains, the dishwasher pumps out, or another fixture is used. The trigger identifies which branch is sending water toward the restriction and helps locate it.
Backup during dishwasher drain points to the kitchen branch
If the sink fills when the dishwasher drains, first check the strainer, disposal if present, trap, and accessible dishwasher drain connection. Disconnect appliance power as required before opening or handling connected components.
Other affected drains suggest a shared restriction
Gurgling at another fixture, water rising in a tub, or several slow drains suggests the problem lies beyond the sink trap. Continuing to treat only the kitchen can miss a developing wastewater backup.
Stop using water if the backup contains wastewater
If dirty water returns, sewer odor is strong, or the level keeps rising, reduce use of connected drains and arrange plumbing service. Avoid contact with backed-up wastewater and treat cleanup as contamination rather than an ordinary spill.