Officials in Houston lifted a boil water notice for the city's main water system on Tuesday. 

"Customers no longer need to boil water before drinking, cooking and making ice. Water quality testing submitted to the Texas Commission on Environmental Quality (TCEQ) has confirmed that tap water meets all regulatory standards and is safe to drink," the city said in a release.

The order had been in effect since Sunday after a power outage at the East Water Purification Plant caused pressure to drop.

The notice, which impacted all of the city of 2 million people and some adjacent areas, was issued out of an abundance of caution.

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The order led to the closure of businesses and schools, including the Houston Independent School District. 

The district canceled classes on Monday and Tuesday.

Mayor Sylvester Turner said that because the issue was within the plant’s system, backup power generators would not have made a difference.

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Since the transformers were down, they couldn’t transmit power to the plant.

Turner also said that the power system at the water plant undergoes regular maintenance and that he has ordered a diagnostic review of the system.

Customers are instructed to flush their water system by running cold-water faucets for at least one minute, cleaning automatic ice makers by making and discarding several batches of ice and running water softeners through a regeneration cycle.

The Associated Press contributed to this report.