Survivors of Tropical Storm Washi in Mindanao are in desperate need of water and sanitation facilities, say aid workers and officials.
"Water for drinking and hygiene purposes is our number-one concern right now," General Benito Ramos, the Philippines' top civil defence official and head of the National Disaster Risk Reduction and Management Council (NDRRMC), told IRIN.
Snehal Soneji, country director for Oxfam in Manila agreed: "Unless we act now, there is a real risk of disease outbreak."
More than 1,000 people were killed and over 640,000 people affected when Washi struck the southern island of Mindanao on 17 and 18 December, dropping the equivalent of one month's rainfall in a day, resulting in massive flooding, flash floods and landslides.
Some 300,000 people were displaced and close to 30,000 homes damaged or destroyed, the NDRRMC reported on 22 December, with more than 43,000 people now in 51 shelters, mostly schools, and another quarter of million staying with relatives or living in makeshift shelters.
"Entire areas were completely flattened; only a few sturdy buildings remain standing, and these had sustained a lot of damage," said acting UN Resident and Humanitarian Coordinator, Dr Soe Nyunt-U, who returned from a two-day visit the area.
Anecdotal evidence on the ground suggests about 80 percent of the affected population do not have access to flowing water, says Oxfam, with one shelter reportedly having only one latrine for 4,000 residents.
"Open defecation is fast becoming an issue which will further exacerbate the risk of disease," Soneji said. "And in a largely urban environment this is particularly problematic."
Broken water supply
But addressing the massive water, sanitation and hygiene needs will prove a challenge.
"The water is there, but with the damage to the booster pumps and wells, the problem now is bringing the water to the beneficiaries in evacuation centres as well as those in the damaged areas," Andres Casal, water and habitat coordinator for the International Committee of the Red Cross (ICRC) in the Philippines, explained.
According to the UN Children's Fund (UNICEF), the water systems of the two main affected areas, Cagayan de Oro and Iligan cities, were totally destroyed, leaving most residents with no safe, reliable source of water.
"The water supply system is essentially broken," Oxfam's Soneji said, while NDRRM's Ramos said damage to the system could take at least a month to repair.
On 22 December, the UN and humanitarian partners called for US$28.6 million to help the survivors.
Under the Emergency Revision of the Philippines (Mindanao) Humanitarian Action Plan 2012, the appeal aims to provide clean water for drinking and bathing, food, emergency shelter, and essential household items to 471,000 worst-affected people in Cagayan de Oro and Iligan for three months.
According to the UN Office for the Coordination of Humanitarian Affairs (OCHA), the humanitarian response plan will be revised within six weeks to reflect evolving needs on the ground.
The Philippine government declared a state of national calamity in the hardest-hit areas on 20 December, accepting international humanitarian assistance.