Sukkur, Pakistan (CNN) -- They are so small that at first you may miss them. Their newborn cries are impossibly soft, asking for their mother's nourishment.
Seven-day-old Rida and Nida, twin girls, are among the youngest of the 900 refugees at a school-turned-refugee camp in Sukkur, Pakistan.
Born after the floods hit Pakistan, they may not be thriving, but they are surviving.
Their mother, Maryum, is grateful her daughters are still alive amid the chaos of Pakistan's worst floods in 80 years, but she does not feel the joy of new motherhood.
"I'm worried about them," said Maryum. "We don't have anything. No clothes, no home, nothing."
Maryum dipped her fingers into a bowl of water and touched Nida's lips. Nida, who is smaller and weaker than Rida, lapped up the water with her small mouth.
"This is the cleanest water we have," Maryum said.
Cleanest does not mean clean. The water at this refugee camp is still untreated, but the children are drinking it in the sweltering heat and humidity.
It's why 18-month-old Zabair is ill with a water-borne disease. A yellow IV remained attached to his small left hand as volunteer doctors tried to treat him.
With enough clean water, many children can recover. The problem in Pakistan's growing humanitarian crisis is access to that clean water.
The U.N. says 3.5 million children are at risk of contracting water-borne illnesses in the wake of these floods. Pakistan's government estimates 500,000 pregnant women are also at risk of falling ill.
Across the country about 20 million people need shelter, food and emergency care.
The United Nations has appealed for $460 million over the next three months. Secretary-General Ban Ki-moon said that although donors delivered more than half, the available resources are not sufficient to meet the needs on the ground.
Mehraan, who delivered a baby girl three days ago, was unable to get access to a doctor and her two-month premature daughter died.
She says fear of the floods took her daughter away. She then clutched her stomach, moaning, "I'm sick, I'm sick."
One of the biggest problems at this refugee camp is sanitation.
Human feces dot the ground, just meters away from where children sleep.
Dr. Ismael Mako is a volunteer doctor trying to help the refugees at the numerous camps in Sukkur.
"Antibiotics, IV's," said Mako, "we need this."
What he's seen among the children and pregnant women are in many cases preventable, easily treated illnesses.
But in this unfolding crisis in Pakistan, he predicts that without more aid soon there will be wave after wave of medical crises.