Shaken residents sought refuge in shelters, while authorities carried out evacuations by air since hundreds of roads and bridges were closed to traffic yesterday.
Some 26,000 South Carolinians did not have electricity and 40,000 had no drinking water, Governor Nikki Haley told reporters on the outskirts of the capital Columbia, which has been especially hard hit.
Haley, who confirmed the latest toll, has called the extreme floods a once-in-a-thousand-year event.
President Barack Obama signed a disaster declaration, which makes federal aid available.
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Covering the counties of Charleston, Dorchester, Georgetown, Horry, Lexington, Orangeburg, Richland, and Williamsburg, the assistance can be used for things such as emergency housing.
Water distribution points were planned for Columbia, since drinking from the city system was considered unsafe after breaches in the canal supplying the city.
Other distribution centers were due to be added around the state in the coming days.
Local media reported firefighters were pumping fresh water to the water systems of Columbia's hospitals, which, like the rest of the city, had been advised to boil water before using it.
The tropical air mass that has drenched the southeastern state since Thursday dumped 14 inches (36 centimeters) of rain over the weekend, a new record, according to the National Weather Service.
That downpour caused sudden and dramatic flooding throughout the state on Sunday, leaving residents scrambling for safety.
"Our house, car -- we lost everything. Everything is underwater. We didn't get time to do nothing," said Patricia Harde, 48, who fled with her two adult daughters and their four small children, including a four-month-old baby, to a school-turned-shelter.
"I went back to try to get things for the baby -- milk and Pampers -- but I couldn't. Everything was covered in water."
Firefighters came to rescue them. But while some rode in a boat, others had to walk through the rapidly rising dirty water.
The water was still rising when they got to firstshelter, so they moved on.