World Water Day is an annual UN observance day (always on 22 March) that highlights the importance of freshwater. The day is used to advocate for the sustainable management of freshwater resources. World Water Day is celebrated around the world with a variety of events. These can be educational, theatrical, musical or lobbying in nature. The day can also include campaigns to raise money for water projects. The first World Water Day, designated by the United Nations, was in 1993. Each year many countries celebrate World Water Day.

UN-Water is the convener for World Water Day and selects a theme for each year in consultation with UN organizations that share an interest in that year's focus. The theme for 2019 is "Leaving no one behind" and encourages people to consider marginalized groups as these are often overlooked and discriminated against when they try to access safe water. Previous themes for the years 2014 to 2018 were "Water and energy", "Water and Sustainable Development", "Water and Jobs, "Why waste water? and "Nature for Water.

The focus on universal access to clean water, sanitation and hygiene (WASH) is in line with the targets of Sustainable Development Goal 6. The UN World Water Development Report (WWDR) is released each year around World Water Day.