Houston has become the latest U.S. city to issue a boil-water advisory after a Sunday morning power outage at a treatment plant caused water pressure to fall below the level required by the Texas Commission on Environmental Quality. The situation in the Texas city affects at least 2.2 million residents’ water supply. “We believe the water is safe but based on regulatory requirements when pressure drops below 20 psi we are obligated to issue a boil water notice,” tweeted the Houston Mayor’s Office on Sunday. [time-brightcove not-tgx=”true”] The city is asking folks to boil water for three minutes before consumption, and reminding people to avoid using chilled water and ice from any appliances connected to the waterline, such as a refrigerator.