Sign up for The Daily Reach, and get all the news that’s fit for your inbox.

CPS Energy intentionally cut off power to some San Antonio Water System pump stations earlier this week as the energy utility struggled to impose demand cuts needed to stabilize the Texas power grid.

San Antonio’s water system is struggling with a drop in pressure, with frozen plumbing, leaks, and a drop in water supplies all contributing to the problem. As of late Wednesday, SAWS estimated that 30% of its customers lacked water service, and it issued a system-wide notice Wednesday to boil drinking water in part because officials were uncertain whether low pressures have drawn unwanted contaminants into the system.

CPS Energy reported significant improvements Thursday morning in reconnecting residents. Utility officials say it is not imposing any controlled blackouts, with fewer than 8,000 remaining households without power mostly because of equipment damage.

But during most severe blackouts amid sub-freezing temperatures Monday and Tuesday, CPS Energy and SAWS decided to cut power to some SAWS pump stations to spare other sites, including hospitals, police and fire stations, and medical research centers, officials said.

“We coordinated with [CPS Energy], recognizing the problem we were creating on the water side, but also acknowledging the challenges they were facing on the electrical side,” SAWS Chief Operations Officer Steve Clouse said Wednesday.

Clouse added that “almost all SAWS facilities are identified as being critical assets within CPS [Energy].”

“In other words, when they turn off a circuit – a large part of town – they know if we have pump station there, and they protect the electrical supply to that pump station, if possible,” he said.

Power cuts during planned blackouts come at the circuit level, with CPS Energy choosing which circuits to shut down and which to remain open. Roughly two-thirds of its system – 250 circuits – is eligible for shutoff.

Another one-third – approximately 125 circuits – is not eligible. These connect to medical facilities and public safety sites, according to CPS Energy.

Maps or detailed drawing of these circuits are closely guarded and kept from the general public. Electric utilities never share details about the exact layout of their systems, citing the vast array of security risks it could pose.

“We will protect that circuit-level information, from that basis alone,” CPS Energy Chief Customer Engagement Officer Rudy Garza told the San Antonio Report earlier this week.

In a call with reporters Thursday, CPS Energy President and CEO Paula Gold-Williams confirmed that most SAWS pumps are on circuits deemed critical. But she added that CPS Energy needed to make such steep demand cuts that it switched off electricity to some circuits on the critical list.

“As the crisis got worse, we in turn had to hit some of those critical circuits,” Gold-Williams said. “Not all of them, but some of them.”

Utility officials at both SAWS and CPS Energy describe the water pump shutoff as a difficult but necessary decision, given the circumstances.

“We didn’t like it, it’s the last thing we would ever want to do, but we realized that people were literally freezing out there and that CPS [Energy] needed to give people more time to allow electrical service to homes,” Clouse said.

However, the issue raises questions of resiliency and whether San Antonio is prepared for similar events in the future.

“It is incredibly difficult for us to run a water system when we’re on a turn-off system like that,” Clouse said.

CPS Energy is a financial supporter of the San Antonio Report. For a full list of business members, click here.

Brendan Gibbons is a former senior reporter at the San Antonio Report. He is an environmental journalist for Oil & Gas Watch.