Meanwhile, in Las Vegas, high temperatures dipped below the 115-degree mark Wednesday for the first time in five days.
For the first time in years, Phoenix homeless shelters opened their doors during the day to offer respite from the blistering sun, which has delivered above-average temperatures every day since June 29. Police began passing out thousands of water bottles donated by grocery stores, and city officials set up tents for shade downtown.
"I don't know why I'm not burnt to pieces," said Chris Cruse, 48, after taking refuge in a shelter.
Four more bodies were found Wednesday, and Phoenix police officer Kathy Ralph tells CBS Radio News the death toll could rise.
"A couple of the people we found have been dead for awhile, and they're in that homeless environment, so it's possible that more could turn up," Ralph said.
Fourteen of the victims were thought to be homeless. Authorities did not know if a man found by the side of a road Sunday had a permanent residence.
The other three victims were elderly women, including one whose home cooling system was not on, police said.
"Most of us just run from air-conditioned box to air-conditioned box, so it's hard to imagine how omnipresent the heat really is for the homeless here," said Phoenix police Sgt. Randy Force.
In all of last year, the state Department of Health Services documented 34 heat-related deaths among Arizona residents. The number of illegal immigrants killed by heat-related illnesses while trying to cross the desert are counted separately.
The first deaths were reported Saturday. By Wednesday, the high still climbed to 109 degrees. Even during the coolest part of the day, the mercury has failed to descend lower than 89 degrees.