A boil water notice was lifted for more than 2 million Houston residents on Tuesday after a power outage affected a local water treatment plant, according to Houston Public Works.
Water quality testing submitted to the Texas Commission on Environmental Quality confirmed the tap water has met all regulatory standards and is safe for human consumption.
Officials told residents to flush their 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.
The water pressure dropped below the Texas Commission on Environmental Quality's required minimum of 20 PSI during a power outage at the East Water Purification Plant on Sunday, according to the agency.
Houston Mayor Sylvester Turner said the water was safe and the boil order was done to comply with regulations. He tweeted that the city submitted its plan to TCEQ to lift the notice Sunday night.
"Water samples will subsequently follow and hopefully we will get the all clear from TCEQ. The city has to wait 24 hours from that point before the boil water notice is suspended," Turner said.
MORE: Map: Where ongoing water crises are happening in the US right nowThe incident had a ripple effect on other city services and organizations.
Houston schools were closed Monday and Tuesday because of the order.
"We will closely monitor the situation and provide additional updates about operations for Wednesday," Houston's Independent School District tweeted Monday afternoon.
Yvonne Williams Forrest, Houston's water director, told ABC affiliate KTRK Sunday night the city's pressure system was below the regulatory limit.
"There are a number of steps in the regulatory process before you issue a boil water notice and we didn't want to unnecessarily alert the city if we did not have to issue a boil water notice," she told KTRK.
Turner said the power outage was caused by two transformers that malfunctioned. Power was restored Monday around 12:15 p.m. local time, he said.
MORE: Video How to keep your water safe during a boil-water advisoryThe mayor said 16 sensors fell below 20 PSI for two minutes, triggering the emergency, and full water pressure was restored above 20 PSI at 14 of the 16 locations.
Turner said the incident will be investigated and he apologized to the city, schools and parents for the cancellations.
"I can't tell you why it failed, stuff does happen and it's unfortunate," he said.