Nearly seven million people in the US state of Texas have been told to boil tap water before consuming it after a deadly winter storm caused power blackouts at treatment facilities.
The huge storm sweeping across the southern US has killed at least 21 people and left millions without power.
Texas has seen widespread blackouts.
Freezing temperatures have also caused water pipes to burst, despite attempts by some homeowners to insulate them from the cold using blankets.
The state’s energy grid has been overwhelmed by a surge in demand as people try to keep warm in some of the coldest temperatures there in more than 30 years – hitting 0F (-18C) earlier this week.
On Wednesday, the head of the Texas Commission on Environmental Quality, Toby Baker, said that issues with water systems were affecting more than 260,000 people in the state.
The mayor of Houston, Sylvester Turner, urged people to switch off their water supplies to prevent pipes from filling with water and bursting when it freezes.
Mr Turner also said that those without power, and unable to boil the tap water, should consume only bottled water for safety.
The extreme weather is forecast to continue until the weekend.