Durham, N.C. - Chemicals used to clean water pipes were inadvertently added to the chilled water system at Duke Law School Thursday evening, affecting the facility's drinking supply on Friday.

Duke officials said workers from Centex Corp. used the chemicals while flushing the lines for a building addition now under construction. They reportedly left on the water and the chemicals backfed into the facility's water system.

Some people drank the water Friday morning before the problem was discovered, with one person complaining in the afternoon of an upset stomach. The manufacturer of the chemicals, ChemTreat Inc., notes on its safety data sheet that they "may cause moderate to severe gastric upset" if ingested.

Duke's occupational and environmental safety office immediately contacted the City of Durham, which gathered samples and delivered them to the city lab for testing. Results are expected early next week. Building manager Catherine Hall said ChemTreat will come Monday to run additional tests.

Centex immediately placed warning signs on fountains and other sources of drinking water Friday morning, then brought in water coolers for students, faculty and others in the building. School officials said people should not drink the water, or use it for coffee or other drinks, until the tests are completed.

The school also urged anyone concerned about the situation to contact Duke's occupational and environmental safety office at 684-3136, or assistant dean Gael Hallenbeck at 613-7277.

Hall said Centex will continue to flush the water system throughout the weekend.