That figure was down sharply from Tuesday's 3.4 million, Monday's 8 million and Sunday's 9 million, or about a third of the state's population.

The storm caused widespread blackouts across Texas, a state unaccustomed to extreme cold, killing at least two dozen people and knocking out power to more than 4 million at its peak.

As of Wednesday evening, "33 Public Water Systems are non-operational, affecting 20,689 Texans," a spokesman for the state's Commission on Environmental Quality told Reuters, adding that 204 counties were reporting issues with their public water systems.

The spokesman said people linked to 853 public water systems were e were being advised to boil water before consuming it, affecting 1.3 million Texans. Some 1,176 previously issued boil water notices had been rescinded, he added.

Once the current crisis is over, the TCEQ plans to examine the ongoing experience to prevent such a disruption from taking place in the future, Executive Director Toby Baker told Reuters on Wednesday.

Texas Governor Greg Abbott pledged on Wednesday to overhaul the state's electric grid operator after a massive blackout left residents without heat, power or water for days.

The Electric Reliability Council of Texas (ERCOT), which manages the flow of power to about 90 per cent of state residents, has faced sharp criticism over its failure to prepare for severe cold. Outages caused billions of dollars of damages to homes and businesses.

Six ERCOT directors have resigned and a board nominee declined a seat after the condemination of the group's performance.

Australian Associated Press