The city says an initial review of data from its real-time monitoring station indicates fuel entered the water on Monday and Wednesday.
It says there have been no measurements above low-alarm thresholds, but the city is proactively opening distribution valves to flush the water.
The city had already confirmed it was investigating after residents complained they could smell fuel in their tap water again.
Its 8,000 people spent nearly two months under a do-not-consume order last fall after fuel was found in the water.
The city says in a release that it believes there may have been left over hydrocarbons that got into the water supply again.
It is asking residents to remove aerators from their taps and to run the water on cold for 20 minutes before 6 p.m. today.
The city is also asking residents to report fuel smells to its water hotline so that staff can collect water samples.
Workers can’t enter people’s homes to test the tap water, however, because the territory is still under a COVID-19 lockdown order.
Instead, samples will be taken at the nearest site to homes that report fuel smells.
“The City continues to proactively screen for petroleum hydrocarbons and (has) increased its weekly laboratory sampling efforts of water produced by the water treatment plant and throughout the distribution system,” the city said in the release.