Secretary-General Ban Ki-moon is using World Toilet Day on Thursday, November 19, to spotlight one of the least talked about and most important contributors to disease and malnutrition: poor sanitation and hygiene that affect about a third of the world's population, the Associated Press reports.

According to the United Nations, 2.4 billion people lack adequate sanitation and nearly one billion have no toilet facilities and are forced to relieve themselves in open areas.

The UN Millennium Development Goals, which are supposed to be achieved this year, call for cutting in half the proportion of the population without access to basic sanitation.

Ban said that by many accounts, this will be "the most-missed target."

That's why the UN launched a "Call to Action on Sanitation" in 2013 and aims to end "open defecation" by 2025, he said.