Unsafe drinking water and poor sanitation kill 4,000 children every day, global health experts said on Friday.

They described the deaths as a “silent humanitarian crisis” and called for immediate action.

“There should be an outcry, from the health community above all, for immediate, concerted efforts to confront the reality that sanitation coverage rates in the developing world barely keep pace with population growth,” said Dr Jamie Bartram, of the World Health Organization (WHO).

Four out of 10 people around the globe do not have access to a simple pit latrine and one-fifth have no source of safe drinking water.

“Far more people endure the largely preventable effects of poor sanitation and water supply than are affected by war, terrorism and weapons of mass destruction,” Bartram said in an article in The Lancet medical journal.

The report was published as part of a review of the Millennium Development Goals, a number of pledges set out in 1990 to improve living conditions in developing nations by 2015.

The researchers said realizing the goals of eradicating extreme poverty, creating primary school education and reducing child mortality would be difficult without solving the water problem.

Half of all hospital beds in the world are filled with people suffering from water-related diseases such as malaria, diarrhea and trachoma, an eye disorder, according to the report.

Tackling the problem means addressing it from all sides.

Bartram pointed to the fragile balance between development and safety when creating reservoirs and irrigation schemes. Crop watering systems can improve nutrition but they also provide a fertile breeding ground for diseases.

“Improving irrigation to avoid standing or slow-moving water and improving disposal of household wastewater can reduce mosquito breeding and transmission of malaria,” he said.