PRUDENCE ISLAND — The longstanding boil-water advisory for customers of the Prudence Island Water District remains in effect while the district completes testing of its new water treatment system.

In a repeat public notice dated Sept. 1, the district said residents should continue boiling water for one minute before using it for drinking, making ice, brushing teeth, washing dishes or preparing food. Bottled water may also be used.

The advisory dates to September 2018, when a routine sample from the district's storage tank tested positive for total coliform and E. coli. Since November 2018, however, the district has conducted 203 tests, all of which were confirmed by an independent laboratory to be free of E. coli. Total coliform was detected in 15 samples and confirmed by repeat testing eight times.

The district has spent years working with the Rhode Island Department of Health to address potential sources of contamination and bring the system into compliance with state requirements.

A major step came Aug. 4, when the district began operating new treatment facilities and delivering chlorinated and filtered water to customers. The $3.8 million project was fully funded by the Rhode Island Infrastructure Bank with full principal forgiveness, meaning no cost to district customers, according to the notice.

For the next two months, the district will calibrate the system and conduct required state monitoring to ensure chlorine levels remain within specified limits.

The boil-water advisory will remain in place until the treatment system receives full approval from the Department of Health. Until then, the district said it will continue issuing notifications every three months.