The advisory remains in effect for Ewing residents, but officials say they expect it to be lifted Thursday night if water samples test clean.
The advisory was issued Monday for five communities: Trenton, Ewing, Hamilton, Lawrenceville and Hopewell.
It came after Trenton's water plant experienced problems treating water due to the high level of the Delaware River from last week's torrential rains. The plant serves about 200,000 customers.
On Thursday, state Environmental Commissioner Bob Martin said his department would work with the city to investigate what happened and correct any deficiencies they identify.