Dirty drinking water and open defecation, particularly in rural areas of many developing countries, are threatening to subvert gains in child survival rates and other health measurements, two major United Nations agencies said Tuesday in a joint report on global progress in sanitation.

The report by the World Health Organization and Unicef, the United Nations Children’s Fund, said one in three people worldwide, or 2.4 billion, still live without sanitation facilities. That includes 946 million people who defecate in the open, raising the risk that reservoirs and wells will be contaminated.

More access to clean drinking water and improved hygiene are among the so-called millennium development goals established by the United Nations in 2000 to help measure improvements in quality of life. They are to be superseded by “sustainable development goals,” a new set of benchmarks to track progress through 2030. Debates on how to reach the new goals will be a major theme of the annual gathering of world leaders before the United Nations General Assembly in September.

The W.H.O.-Unicef report noted that access to cleaner drinking water had improved markedly in recent years and that child survival rates had advanced as well. Today, fewer than 1,000 children younger than 5 die each day from diarrhea caused by inadequate water, sanitation and hygiene, compared with more than 2,000 in 2000.