Kevin Randal, a construction worker in Houston, has his routine.

Mr. Randal, 60, who works on air conditioning, roofing, flooring and kitchens, spent Saturday inside an attic, drenched in sweat in 100 degree temperatures, fixing an air conditioning unit.

He takes breaks every 20 minutes, drinks a mix of lime juice, salt and water to keep him hydrated and takes little sips of water to prevent nausea and throwing up, he said.

“If you don’t calculate time correctly, you will faint,” Mr. Randal said, adding, “The heat comes and goes, and the jobs come and go with it.”

But for now, the heat is mostly coming and staying.

An onslaught of record heat that shows no sign of easing has united all strata of society with the same fundamental purpose of staying cool, comfortable and safe, while putting particular strains on the poor and those without air conditioning.

And the soaring temperatures are highlighting the risks to Texas, its power grid and its residents as the state and globe continue to warm over time.

In Hutto, a rapidly growing suburb 30 miles north of Austin, Liz Garner and Jona Becerra, Williamson County paramedics, find themselves rushing to an increasing number of heat emergencies from their headquarters at Fire Station No. 1.

On one recent day, Ms. Garner rescued a construction worker in his twenties who had suffered a heat stroke, hurriedly placing him in an ice bath to lower his body temperature after it had climbed to 105 degrees. The heat index that day was 106 degrees.

Outdoor workers and older adults have been deemed particularly vulnerable, but the latest Texas heat wave is gripping everyone in some way. In Houston, residents in the city’s large immigrant community described a broad range of challenges as temperatures began to climb past 100 degrees amid debilitating humidity.

“I have to take it slow so my heart rate doesn’t rise,” said Sandra Tobar, who has worked in landscaping for over 20 years since coming to the United States from El Salvador. She starts working at 6:45 a.m. and typically doesn’t finish until 6 p.m.

“We eat every day so we have to work every day,” said Ms. Tobar, who is in her 50s. “If we don’t work, then we don’t have food. “

Advisories from the National Weather Service have hardly pulled punches in forecasting what’s ahead for Texans and residents of surrounding states in coming days, releasing advisories such as “dangerous heat continues” and “excessive heat warning” with projected heat indexes of up to 120 degrees.

On Saturday, high temperatures exceeding 100 degrees were reported in Austin and San Antonio, with the Houston area recording temperatures of just under 100 degrees. San Angelo in West Texas and Cotulla in South Texas each reached 108 degrees.

“Heat advisories and potentially areas of excessive heat warnings are expected each day through this week for most if not all of south-central Texas,” The National Weather Service said on Sunday.

The extreme heat and humidity is projected to continue in Texas for much of this week, before it spreads into parts of the Southwest and the lower Mississippi River Valley through the Fourth of July weekend.

Cities throughout Texas have opened cooling stations in libraries and other public buildings, many of which have served as shelters for homeless residents. Relief agencies have also accelerated their service. In San Antonio, Pete Barrera, outreach coordinator for Haven for Hope, which works with people who are homeless, drove through the city’s downtown streets on Saturday in a pickup truck loaded with everything from cold water and snacks to food and clothing.

“People are hungry,” he said from his cellphone as he made the rounds. “They’re human beings and they need you. If I can help them, I’m going to help them.”

Texans generally seem to be adhering to agencies’ advice to drink plenty of water, limit outdoor activities, work early or late in the day and wear plenty of sunscreen. State Representative Trey Martinez Fischer, reached at his home in San Antonio last week, reported that he was getting up early and staying hydrated, but said he worried about the impact on tourism at San Antonio attractions such as the Alamo and the downtown River Walk.

“It’s 100 degrees in the shade,” the Democratic lawmaker said.

Law enforcement officers may be dealing their own added comfort challenges. Sgt. Edward Mora of the Hutto Police Department was wearing protective gear weighing more than 20 pounds as he drove through the community in his patrol SUV, awaiting normal police calls as well as being alert for any signs of heat-related problems. “You’re just looking to see how people are doing,” he said.

On Austin’s downtown row of nightclubs on Sixth Street, the temperature was 99 degrees at 7:45 on Saturday night but foot traffic was nevertheless respectably brisk, and compared with the daytime highs, some patrons regarded the latest reading as a welcome cooling off.

Many were wearing shorts and T-shirts, and several said they were following officials’ advice to stay hydrated, though perhaps with a bit of an adjustment. As Angelica Nunez, a real estate agent in Austin, entered a nightclub and restaurant with her husband, Joseph Nunez, she said they were “drinking a lot of water.” She added, “And beer, too.”

Anna Betts contributed reporting.