The northern city has been without steady running water for several weeks after damage to pipelines by heavy bombardment, including suspected strikes by the US-led coalition.
Civilians dehydrated by the blistering summer heat are venturing out to the Euphrates and makeshift wells around the city.
But as fighting between ISIS and advancing US-backed forces ramps up, that journey can be life-threatening.
"I went to pump water from a well in the city's south, close to the river," said Karim, an activist with the Raqqa24 network who remains inside the city.
He spoke to AFP using a pseudonym for fear of being targeted by ISIS, which still controls most of Raqa.
The terrorists had sealed the street between the southern district and the Euphrates, so he and other men gathered around a borehole drilled by a resident.
"We were able to get water for an hour, but then we had to run away because of artillery fire. A shell landed just 50 metres (yards) away from me," he said.
He described a hellish scene: families lugging jerry cans through Raqa's streets, suddenly scrambling for cover from incoming mortar fire and air strikes.
Civilians who managed to escape Raqa have also told AFP they came under IS sniper fire as they tried to fill up buckets from the Euphrates.
With temperatures reaching a scorching 46 degrees Celsius (114 Fahrenheit), Karim said Raqa residents are caught between their extreme thirst and the risky journey to quench it.
"The shortages are killing us. Cold water is the stuff of dreams."
'Dying of thirst'
Since ISIS overran Raqa in 2014, the city has become synonymous with the group's horrific practices, including public beheadings.
With help from the US-led coalition, an alliance of Kurdish and Arab fighters called the Syrian Democratic Forces is waging a fierce assault to oust ISIS from the city.
Years ago, Raqa benefited from its prime location in the fertile river valley, as well as from nearby hydro-electric dams that generated power for much of Syria.
That makes the current water shortages particularly painful, said activist collective Raqqa Is Being Slaughtered Silently (RBSS).
"The deepest irony lies in the fact that this city on the bank of the bountiful Euphrates River is currently dying of thirst," said the group, whose members publish news from activists inside the city.
According to RBSS, at least 27 people have been killed by coalition air strikes in recent weeks as they tried to reach the Euphrates or nearby wells for water.
"My uncle and seven children were killed about two weeks ago as he was heading to a school near the city centre where there was a well," said RBSS co-founder Abdalaziz al-Hamza.
And those who manage to successfully draw water from the Euphrates also face health risks.
The UN warned earlier this month that Euphrates River water was potentially "unfit for consumption" and carried "the risk of water-borne diseases".
"Raqa's population is using the water for everything -- showers, drinking, everything," said RBSS activist Hussam Eesa.
"But it isn't clean, particularly because of all the (mortar) shells and corpses that are in it," Eesa told AFP.
RBSS says it has documented symptoms of water-borne diseases among those who are drinking the river water, including fever and loss of consciousness that the group fears could point to cholera.
The World Health Organization has also documented one child who was paralysed in Raqa by a strain of polio that originates from a vaccine carrying small amounts of weakened but live virus.
Oral polio vaccine (OPV) replicates in the gut and can be passed to others through faecal-contaminated water -- meaning it won't hurt the vaccinated individual, but could infect their neighbours in places where hygiene and immunisation levels are low.