Houston has lifted its boil water notice, two days after a power outage affecting one of the city’s water purification plants raised concerns about contaminants potentially lingering in the main water supply. The Texas Commission on Environmental Quality conducted water quality tests while the notice was still in effect, and confirmed that tap water meets regulatory standards, the city of Houston said in a news release.

“Houston Water has taken the necessary corrective actions to restore the quality of the water distributed by this public water system used for drinking water or human consumption purposes,” the city said.

Before returning to normal use, Houston Water customers should first “flush” their home water systems by running faucets on cold for at least one minute, and making and discarding several batches of ice from their automatic ice machines to trigger water treatment softeners through a regeneration cycle, according to the city.

All of Houston’s public schools will remain closed for a second day Tuesday, after which millions of residents were advised to boil their drinking water in the aftermath of a power outage at one of the city’s purification plants.

Houston officials issued a formal boil water notice on Sunday, when the outage caused water pressure at the East Water Purification Plant — which feeds into the city’s main water system, serving about 2.2 million customers — to drop below regulators’ required minimum of 20 PSI. Lower water pressure at the purification plant increases the risk of bacteria and other harmful microbes