City officials said the water line that burst provides water to 40-50 percent of Houston residents.
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Mayor Sylvester Turner issued an advisory urging residents to boil water before use. The notice, issued to most of the city, will last 24 hours.
Many schools have also closed down Friday.
ABC13 spoke with environmental toxicologist Dr. Noreen Khan-Mayberry, also known as "Houston's Tox-Doc" about questions the public might have about why boiling water is necessary, how to properly do it and when it is needed.
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