By Dennis Romero -
NBC News
Authorities in Houston, the fourth-largest city in the country, urged residents on Sunday to boil their water because the pressure of the pumped water system dropped due to a power outage, raising concerns about possible contamination.
The announcement to boil water affects the 2.3 million inhabitants of the Texan city.
Bottled water is an acceptable substitute, according to municipal public works officials.
The Houston School District announced school closures Monday, which could be extended depending on how quickly the water issue is resolved.
"We will closely monitor the situation and provide additional updates," the district said.
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Mayor Sylvester Turner said in a statement Sunday that the city has submitted a plan to the Texas Commission on Environmental Quality seeking approval to lift the alert.
The city will have to comply with the boil water recommendation, at least until Monday night, 24 hours after the first announcement.
"We believe the water is safe, but with regulatory requirements, when the pressure drops below 20 psi we are required to issue a boil water advisory," Turner said.
Texas Gov. Greg Abbott said he was pushing to expedite the results of water tests and analysis that could end the boil notice.
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"We are working to satisfy the city's request for assistance with prompt delivery of water sample results," he said in a statement.
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A power outage Sunday at the Eastern Water Purification Plant caused pressure to drop below 20 psi, or pounds per square inch, the state threshold that triggers boil water advisories, Houston Public Works said.
Soon after, water pressure was restored to acceptable levels in the city, but if there was contamination during the low pressure episode, it could still be traveling through the system, explaining why a boil advisory was in effect despite the satisfactory pressure.
The pressure of the water system can use the weight of the 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 watches, particularly diving watches, to increase resistance to leakage, as the pressure builds underwater and pushes against joints and parts.
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In early 2021, Houston Public Works explained that its system is not as reliant on gravity as those in other large cities.
"Houston's water system is different from other systems in that we don't use water towers to provide pressure to the system. We use onshore storage tanks and pumps," he tweeted.
It is not clear what caused the outage on Sunday morning.
The water purification plant is outside the city, in Galena Park.
CenterPoint Energy, the utility that serves the area around the plant, said in a statement that the power outage was not the result of its service and may have been caused by a problem at the facility.