Preventable water-related illnesses could kill as many as 76 million people by the year 2020 unless nations take action to improve their water-delivery systems, according to a report by a California environmental research institute. Most of the affected people would likely be children in developing countries, who are highly susceptible to such water-borne diseases as diarrhea, worms, dysentery, and cholera. Experts estimate that currently, 2 to 5 million people die every year from water-related illnesses; the new study blames those deaths largely on development efforts that have focused on big, centralized water-delivery systems rather than accessible, affordable, localized methods of providing clean water to impoverished people. Peter Gleick, lead author of the study, called the issue “a hidden tragedy” and “one of the greatest development failures of the 20th century.”