HOUSTON, Texas (KTRK) -- The boil water notice for the City of Houston has been lifted after testing determined the tap water is safe to drink.
Houston Public Works made the announcement at 6:40 a.m. on Tuesday.
Officials said customers no longer need to boil water before drinking, cooking, and making ice after water quality testing submitted to the Texas Commission on Environmental Quality confirmed that tap water meets all regulatory standards and is safe to drink.
The city said Houstonians should 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.
Anyone with questions about water safety can contact 311 or (713) 837-0311.
The City of Bellaire rescinded its boil water notice Monday night, saying Houston's water system didn't impact its water quality.
Houston ISD and a number of other school districts canceled classes on Tuesday, for the second day in a row, due to the boil water notice.
ABC13 asked city officials how this all happened in the first place.
They say it's something they're still working to investigate and can hopefully prevent from happening again.
Officials say it all started when three plants inside the East Water Purification Center lost power at 10:50 a.m. Sunday.
That triggered the water pressure to fall below the emergency standard of 20 PSI, where bacteria can grow more easily.
Houston Mayor Sylvester Turner said city officials consulted with the state, but the boil water advisory was not issued until seven hours later, around 6:40 p.m.
He said a transformer at the water center also failed, as well as the backup transformer.
The city has a long-standing $56 million contract with NRG Energy Services for backup power generators.
NRG told 13 Investigates that the problem was with the two city-owned transformers.
"I know some people have said on social media, 'What about the generators?' Well, we did have generators. But when the transformers failed to operate, it prevented the generators from being connected in order to provide the additional power," Turner explained. "Plus, there was still power in the grid. So it was the transformers in between the grid and the generators that prevented the power."
Turner said the power was out for two hours.
He said the water pressure dropped below the emergency standard for less than two minutes, but the boil water advisory was put in place out of an abundance of caution.
The incubation period takes about 18 hours, so the order could only be lifted once the final official results came in.
A spokesperson for the mayor's office contacted Eyewitness News through email.
"It turns out that it was a Centerpoint Energy contractor, ESG Energy Systems Group, that evaluated over 230 critical infrastructure sites, which included all water and wastewater sites. ESG evaluation looked at grid power and backup generation. They did not perform any operational or maintenance evaluation. However, ESG informed the city that with double redundancy, this Tier 1 site is already well hardened."
13 Investigates requested nearly two years' worth of inspection reports for the East Water Purification Plant, including the transformers that failed.
We also asked for emails and texts between the mayor and the city's office of emergency management to hopefully learn more about the conversations around when to notify the public.