HOUSTON (AP) -- More than 2 million people in the Houston area were urged to boil their tap water Monday after a power outage at a purification plant prompted the mayor to initiate a review of what went wrong.
The boil order notice tells customers in the nation's fourth-largest city to boil water before it's used for cooking, bathing or drinking. Multiple Houston-area public and private schools, as well as some local colleges, were closed Monday as a result of the notice, while others made adjustments to provide affected campuses with bottled water and sanitizer.
Houston Independent School District officials said in a Monday afternoon statement that closures would continue through Tuesday due to "the logistical challenges caused by the notice."
"Those challenges prevent the district from being able to provide meals for its students and ensure safe water is available for students and staff," Houston ISD officials said in a statement.
The notice was issued Sunday, hours after two transformers failed, causing power outages at the water plant, Houston Mayor Sylvester Turner said at a press conference Monday. There was no indication the water system had been contaminated.
Water quality testing was underway, Turner said. He said he expects the notice to be lifted by early Tuesday at the latest, once the state's environmental agency gives an all-clear after analyzing test results.
"We are optimistic the results will come back clean," Turner said.
According to Turner, the city issued a notice, which affects all of Houston and multiple adjacent areas, in an "abundance of caution" after the two transformers -- a main one and its backup-- "uniquely and coincidentally" failed. The problem affected the plant's ability to treat water and pump water into the transmission system, resulting in low water pressure.
Because the issue was within the plant's system, backup power generators would not have made a difference, Turner said. Since the transformers were down, they couldn't transmit power to the plant.
The power system at the water plant undergoes regular maintenance, Turner said, but he did not give a timeline for how often. The mayor said he has ordered a diagnostic review of the system to understand how this was possible and how it can be prevented.
Sixteen sensors marked dips under the minimum pressure levels required by the Texas Commission on Environmental Quality -- 14 of them for only 2 minutes and two of them for nearly 30 minutes, Turner said.
Typically, there's enough pressure for water to flow out of leaky pipes. When pressure is lost, however, contamination like bacteria sitting near pipes can be sucked into the system, creating a health risk.
Reliable electricity is a top priority for any water system that must move vast amounts of heavy water through the treatment plant and to people, said George Hawkins who ran Washington DC's water provider for about 8 years.
"The issue I feared the most was power loss," he said. Like Houston, Hawkins said an electric failure once forced part of Washington DC to temporarily boil its water.
Officials later conducted a review to ensure there were enough redundancies in the power supply to keep safe water flowing during electric grid outages and major storms.
After a water pressure loss, potentially contaminated water is typically flushed out of pipes and faucets. If tests for contamination are negative, the boil water notice can be lifted, said Hawkins, who now runs Moonshot Missions, a nonprofit focused on improving water services in disadvantaged areas.
Tony Crawford said he hurried to buy water after he heard about the boil notice, as he loaded three cases of bottled water into his vehicle outside a Houston Walmart.
"I have pets, so I decided to come up here and get water," Crawford said. "It's never been a water issue for me until today."
In a statement Monday, officials from the Memorial Hermann Health System said they activated boil water notice policies and procedures at affected facilities to "allow the system to remain operational under enhanced engineering controls and infection prevention supervision."
"With the exception of a few minor delayed starts to elective surgeries on Monday morning," all Memorial Hermann locations are open and operational, according to a statement from Memorial Hermann Health System.
U.S. Rep. Sheila Jackson Lee, a Democrat who represents parts of Houston, helped distribute water at a flu vaccination site in partnership with a local wellness center, providing water to everyone who received a shot.
The National Association of Christian Churches set up a separate water giveaway, with a limit of one pack of water per household.
Turner defended the decision to warn residents about the water quality several hours after the issue first occurred and apologized for the disruptions to businesses, schools and elective surgeries. He said the dip in pressure did not automatically trigger a water boil notice, but a decision was made to issue one based on the data once the city consulted with and was instructed to do so by TCEQ.
The city will also review how residents were informed of the notice to boil water, Turner said.
Water infrastructure and quality has been a prominent issue in cities large and small throughout the U.S., including Baltimore; Honolulu; Jackson, Mississippi; and Flint, Michigan.