PABBI, Pakistan (AP) — Five-year-old Shahid Khan struggled to remain conscious in his hospital bed as severe diarrhea threatened to kill him. His father watched helplessly, stricken at the thought of losing his son — one of the only things the floods had not already taken.

The young boy is one of millions of children who survived the floods that ravaged Pakistan over the last month but are now vulnerable to a second wave of death caused by waterborne disease, according to the United Nations.

Khan’s father, Ikramullah, fled Pabbi just before floods devastated the northwestern town about a month ago, abandoning his two-room house and all his possessions to save his wife and four children.

“I saved my kids. That was everything for me,” said Ikramullah, whose 6-year-old son, Waqar, has also battled severe diarrhea in recent days. “Now I see I’m losing them. We’re devastated.”

Ten other children lay in beds near Khan at the diarrhea treatment center run by the World Health Organization in Pabbi, two of whom were in critical condition.

Access to clean water has always been a problem in Pakistan, but the floods have made the situation much worse by breaking open sewer lines, filling wells with dirty water and displacing millions of people who have been forced to use the contaminated water around them.

The environment is especially dangerous for children, who are more vulnerable to diseases such as diarrhea and dysentery because they are more easily dehydrated. Many children in Pakistan also suffered from malnutrition before the floods hit, leaving them with weakened immune systems.

The Pakistani government and international aid groups have worked to get clean water to millions of people affected by the floods and treat those suffering from waterborne diseases. But they have been overwhelmed by the scale of the disaster, which has displaced a million more people in recent days.

The floods started in the northwest in late July after extremely heavy monsoon rains and surged south along the Indus River, killing more than 1,600 people, damaging or destroying more than 1.2 million homes and inundating one-fifth of the country — an area larger than England.

Some 3.5 million children are at imminent risk of waterborne disease and 72,000 are at high risk of death, according to the United Nations.

The World Health Organization set up the diarrhea treatment center in Pabbi about a week ago with the help of several other aid groups.

Workers have already treated more than 500 patients, mostly children, said Asadullah Khan, one of the doctors.

The aid groups set up a similar treatment facility several days ago in Nowshera, a city adjacent to Pabbi that was also engulfed by the floods. Residents who have begun to return in recent days have encountered a scene of total destruction: caved-in houses and streets covered with mud and debris.

Most of the population lacks access to clean water, and mosquitoes have proliferated in stagnant floodwater around the city, raising the risk of malaria. Government help is nowhere to be found.

“It is trash, dirt, germs and odd smells everywhere,” said Zahid Ullah, whose 3-year-old and 10-year-old sons were being treated for gastroenteritis at the facility in Nowshera. “It is a big danger.”

Even at the hospitals where the diarrhea treatment centers have been set up, mobs of flies hovered around the patients despite attempts by staff to kill them.

The World Health Organization and the United Nations Children’s Fund appealed to the world on Saturday to provide water purification units, family hygiene kits and other items needed to increase access to clean water in Pakistan.

Guido Sabatinelli, the head of the World Health Organization in Pakistan, said the international community’s help was critical to help Pakistan avoid a second wave of death from waterborne disease.

“We are fearing the epidemic of disease,” said Sabatinelli. “Access to safer water, potable water” is critical, he said.

Asma Bibi couldn’t agree more. The young mother searched in vain for clean water on the outskirts of Nowshera as her feverish 2-month-old son, Ehtesham, sweltered in a tent set up for flood victims. They had run out of water the day before.

“My son is sick. He hasn’t breast-fed in two days,” she said. “He needs milk. He needs water.”