At a Glance Power outages knocked out water plants.
Houston is under a boil water advisory, and officials asked that water be conserved for essential use only.
At least 77 people were treated for hypothermia in northern Texas.
Houston residents woke up Wednesday morning with little or no water pressure, on top of a third day of widespread power outages that have left millions without heat amid frigid temperatures and back-to-back winter storms.
Harris County Office of Emergency Management said the water issues are due to the ongoing power outages.
"Nearly (all) parts of the county are experiencing low water pressure - or have none at all," the agency tweeted. "Water utilities are struggling to operate in light of the state power issues. This will not improve until more power is restored."
In many areas, including the city of Houston, those with water are being advised to boil it before drinking. Those without power – 360,000 homes and business in Harrison County alone – are being told to use bottled water.
Harris County Judge Lina Hidalgo, who oversees emergency management, called the combined water and power outages "a nightmare." Hidalgo said all residents should assume they are under a boil water notice.
Officials asked that water be conserved for essential use only.
"Conserving water will allow us to save water for firefighting operations and other life-safety items," the Office of Emergency Management tweeted.
In some cases, it was so cold overnight that water from burst pipes or running faucets froze inside homes. One residents said he used melted snow to flush toilets.
(MORE: Here's When the South Will Finally Thaw After Record-Smashing Cold, Snow and Ice)
The water outages come as first responders in Texas respond to hundreds of calls related to hypothermia and carbon monoxide poisoning, and officials can't say for sure when electricity might be fully restored.
Water outages also affected hundreds of thousands of residents Tuesday in several other areas, including Abilene and Fort Worth.
Back to back winter storms, combined with the year-long coronavirus pandemic that hit Texas worse than many other states, are pushing residents to their limits.
“To go through all of that and then also to have stuff like this happen, it’s like, ‘One more historical event, and I’m going to develop PTSD,’” Brianna Blake, 31, a mother of two sons, told the Texas Tribune. “I cannot do this.”
In Houston, residents like Natalie Harrell, her boyfriend and four kids took shelter at a furniture store that provided people with food, water and power to charge electronics.
“It’s worse than a hurricane,” Harrell told The Associated Press.
Advertisement Nearly 2.5 million homes and businesses remained without power in Texas Wednesday morning, according to poweroutage.us. That was down from well over 4 million at the peak of the outages so far, which started Sunday night as power plant equipment began to freeze and demand surged. Electricity providers were forced to initiate rolling blackouts in order to keep the entire grid from failing.
Now, no one knows how long the outages will last.
"The biggest variable that makes it difficult to give you a certain answer ... we're relying on ability to get that supply and demand in balance," Bill Magness, president and CEO of Electric Reliability Council of Texas, told reporters during a news conference Tuesday afternoon.
(MORE: Why Winter Storm Uri Caused Millions of Power Outages in Texas)
Hypothermia and carbon monoxide poisoning cases continue to rise as the dire conditions drag on.
MedStar, which provides ambulance service for Fort Worth and 14 other towns in northern Texas, treated 77 patients for hypothermia on Tuesday and eight for carbon monoxide poisoning.
Harris County Judge Lina Hidalgo said Tuesday that at least 300 calls regarding carbon monoxide poisoning had been received by the fire marshal, hospitals and other agencies. Hidalgo called it a "disaster within a disaster."
The Cy-Fair Fire Department in northwest Harris County said many people were using charcoal grills inside their homes for heat. The department took 14 people, including seven children, to hospitals because of carbon monoxide poisoning.
In Fort Worth, Cook Children's Medical Center treated at least 13 pediatric patients for carbon monoxide poisoning.
At least 10 people in Texas have died in weather-related incidents since Sunday, including a mother and a child due to carbon monoxide poisoning. The deaths of at least eight people in several other states this week are also being blamed on the weather.
The back to back storms, named Uri and Viola by The Weather Channel, created hazardous travel conditions in Texas and other states.
A portion of Interstate 20 eastbound in northwestern Louisiana was closed Wednesday morning.
These are unprecedented times, and we need the communities’ assistance and cooperation," Louisiana State Police said on Facebook. "Roadways remain impassable around our area, and we urge motorists to please avoid all unnecessary travel."
Motorists struggled on icy roads in Austin.
Ongoing power outages continued in several other states Wednesday morning, including more than 157,000 in Oregon, 100,000 in Kentucky, 71,000 in West Virginia and 49,000 in Louisiana.
1/47 Arrow Left Arrow Right Morgan Handley, left, tries to convince people to come to move to a warming shelter to escape sub-freezing temperatures, Tuesday, Feb. 16, 2021, in San Antonio. (AP Photo/Eric Gay)
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Ice and snow cover a shopping center parking lot in Tyler, Texas (US).
A series of winter blasts have struck the US state of Texas in recent days, leaving at least ten people dead in the aftermath.  On Wednesday, the second wave of the storms impacted utilities and water systems, with cities asking citizens to conserve water usage.  Reports early Wednesday indicated more than two and a half million homes and businesses were without power.  Texas is the only one of the 48 contiguous US states with its own separate .

One media source indicated   killed a mother and her child in the city of Houston.  A house fire killed a woman and three children in the city of .  The storm has impacted shipments of COVID-19 vaccine, according to at least one report.  Citizens were asked to conserve usage of electricity where possible.  Reports from the city of Tyler indicate roads were nearly impassible on Monday and Tuesday due to ice and snow.

Earlier in the month, winter conditions contributed to a massive vehicle pile up in the city of , taking the lives of at least five people.  Some victims were trapped in their vehicles for hours, awaiting rescue.  During a press briefing, an emergency services official said this was a once-in-a-lifetime event.