Residents of the country’s fourth-largest city were told to boil their water on Sunday after pressure in the pump-driven water system dropped due to a power outage, raising concerns about possible contamination.

The boil advisory essentially covers all of 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 schools would be closed to employees and students Monday and the closure could be extended depending on how quickly the water issue is resolved.

«We will be closely monitoring the situation and will provide additional updates tomorrow,» the district said in a statement.

Houston 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 advisory.

The earliest the city could be released from the boil requirement would be Monday night, 24 hours after the notice was posted, he said.

«We believe the water is safe, but under 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 expediting the city’s request to expedite the results and analysis of water tests that could end the boil advisory.

«We are currently working to meet the city’s request for assistance with a rapid response to the results of the water samples,» he said in a statement.

A power outage Sunday at the eastern water purification plant caused pressure to drop below 20 PSI, the state threshold that triggers boil water advisories, Houston Public Works said.

Not long after, water pressure was restored to acceptable levels in the city, but if there was contamination during the low pressure episode, it may still be traveling through the system, which explains why a low pressure advisory was in effect. boiling despite 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, namely diving watches, to increase resistance to leakage as pressure builds underwater and pulls seals and parts together.

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,» he said. tweeted. «We use ground-based pumps and storage tanks.»

It is not clear what caused the outage on Sunday morning. The Eastern Water Purification Plant is outside of town, in Galena Park, Texas. 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.

joe studley Y lindsey pipia contributed.