Residents of the country's fourth-largest city were told to boil water Sunday after pump-driven water system pressure dropped because of an electrical outage, triggering concerns of possible contamination.
The boil notice essentially covers Houston's 2.3 million residents. Bottled water is an acceptable substitute, public works officials said in a statement.
The Houston Independent School District said that schools would be closed to employees and students Monday and that the closure could be extended depending on how fast the water problem is resolved.
"We will closely monitor the situation and provide additional updates tomorrow," the district said in a statement.
Mayor Sylvester Turner said in a statement late Sunday that the city is submitting a plan to the Texas Commission on Environmental Quality seeking approval to lift the boil notice.
The earliest the city could be liberated from the boil requirement would be Monday night, 24 hours after the notice was published, he said.
"We believe the water is safe but based on regulatory requirements when pressure drops below 20 psi we are obligated to issue a boil water notice," Turner said.
Texas Gov. Greg Abbott said he was expediting the city's request to fast-track the water test results and analysis that could end the boil notice.
"We're currently working to fulfill the city's request for help with rapid turnaround of water sample results," he said in a statement.
A power outage Sunday at the East Water Purification Plant caused pressure to drop below 20 psi, or pounds per square inch, the state threshold that triggers boil water notices, Houston Public Works said.
Not long afterward, water pressure was restored to acceptable levels in the city, but if there was contamination during the low-pressure episode, it might still be traveling through the system, explaining why a boil notice was in effect despite satisfactory pressure.
Water system pressure can use the weight of liquid to occupy cracks and crevices that might otherwise be exposed to outside incursions, such as urban runoff. Similarly, hydraulic pressure is sometimes used in timepieces, specifically dive watches, to increase resistance to leaks as underwater pressure increases and pushes seals and parts together.
In early 2021, Houston Public Works explained that its system is not as dependent on gravity as those in other big cities.
"Houston’s water system is different than other systems in that we don’t use water towers to provide pressure to the system," it tweeted. "We use ground storage tanks & pumps."
It's not clear what caused Sunday morning's outage. The East Water Purification Plant is outside the city, in Galena Park. CenterPoint Energy, the utility serving the area around the plant, said in a statement that the power outage was not a result of its service and that it may have been caused by an issue at the facility.
This article was originally published on NBCNews.com