More than 100,000 residents in El Paso, Texas were left with little to no water after a main break late Saturday night, officials said. The disruption was expected to take until midweek for operations to return to normal, according to the officials.

The break occurred in a 36-inch water main line, El Paso officials said. El Paso has a population of about 700,000, officials said.

After the break, officials issued a boil water notice and set up water distribution centers for residents. Trejo said the situation was intensified by the pipeline’s design and how smaller lines connect to it.

Speaking as an official with El Paso Water, Gilbert Trejo described the break as “an event of unprecedented proportion.” He added that it was made even more impactful by “the way the pipeline itself was designed along with how different connections of smaller lines were made to it.”

Trejo said about 38,000 customer connections were put out of service because of the break, which he said translates to over 100,000 residents impacted. He also said more than 15 water reservoirs “essentially drained out.”

Trejo said there was not enough information yet to determine what caused the break. He asked for patience as crews repair the damage and go through the process to get water flowing again.

The outage also affected local schools. Classes were canceled Monday at more than a dozen schools in the El Paso Independent School District due to the outage, while other schools remained open but were under the boil water notice.