"Each year lack of toilets causes 200 million tons of human waste to go uncollected and untreated around the world, fouling the environment and exposing millions of people to diseases," the organisation said on its website.
"November 19th is World Toilet Day, a day on which we can remind others the importance of better sanitation for EVERYONE."
The group, known by its initials "WTO" says it is a global network of 151 toilet and sanitation organisations in 53 countries.
World Toilet Day "is now being celebrated by members all over the world," the website said.
In its Toilet Day message, the WTO said 2.5 billion people in the world lack access to proper toilet facilities.
The WTO was founded by Singaporean entrepreneur Jack Sim, who has described himself as "something like an evangelist" when it comes to toilets. He could not be reached on Wednesday.
WTO has also organised World Toilet Summits for academics and other experts to discuss toilet-related issues. Sim is also director of the World Toilet College which offers training in toilet maintenance and related matters.