HOUSTON (KIAH) — The City of Houston has lifted its boil water notice after 50-plus hours when a power failure at a water purification plant caused triggered the notice on Sunday night.

The Texas Commission on Environmental Quality said that water quality testing submitted by the city met all regulatory standards and is now safe for Houston residents to drink without boiling water.

Houston Public Works asks customers to flush their water system by running cold-water faucets for at least one minute, cleaning automatic ice makers by making and discarding several batches of ice and running water softeners through a regeneration cycle.

 A power failure at the East Water Purification Plant on Sunday morning caused a drop in PSI at the city’s main water plant later that day, forcing the city to issue a boil water notice out of caution.

The notice was issued around 9:30 p.m. Sunday, and was lifted just before 7 a.m. Tuesday.

At a news conference Monday, Mayor Sylvester Turner said the city issued the notice, which affects all of Houston and some adjacent areas, in an “abundance of caution” after two transformers — a main one and its backup — “uniquely and coincidentally” failed at a water plant. The problem affected the plant’s ability to treat and pump water into the transmission system, resulting in low pressure.

Because the issue was within the plant’s system, backup power generators would not have made a difference, Turner said. Since the transformers were down, they couldn’t transmit power to the plant.

The power system at the water plant undergoes regular maintenance, Turner said, but he did not give a timeline for how often. The mayor said he has ordered a diagnostic review of the system to understand how the problem was possible and how it can be prevented.

Sixteen sensors marked dips under the minimum pressure levels required by the Texas Commission on Environmental Quality, 14 of them for only 2 minutes and two of them for nearly 30 minutes, Turner said.

Typically, there is enough pressure for water to flow out of leaky pipes. When pressure is lost, however, contamination like bacteria sitting near pipes can be sucked into the system, creating a health risk.

 The Associated Press contributed to this report.