World Water Day has been observed on 22 March since 1993 when the United Nations General Assembly declared 22 March as World Day for Water.

This day was first formally proposed in Agenda 21 of the 1992 United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro, Brazil. Observance began in 1993 and has grown significantly ever since; for the general public to show support, it is encouraged for the public to not use their taps throughout the whole day, the day has become a popular Facebook trend.

The UN and its member nations devote this day to implementing UN recommendations and promoting concrete activities within their countries regarding the world's water resources. Each year, one of various UN agencies involved in water issues takes the lead in promoting and coordinating international activities for World Water Day. Since its inception in 2003, UN-Water has been responsible for selecting the theme, messages and lead UN agency for the World Day for Water.

In addition to the UN member states, a number of NGOs promoting clean water and sustainable aquatic habitats have used World Day for Water as a time to focus public attention on the critical water issues of our era. Every three years since 1997, for instance, the World Water Council has drawn thousands to participate in its World Water Forum during the week of World Day for Water. Participating agencies and NGOs have highlighted issues such as a billion people being without access to safe water for drinking and the role of gender in family access to safe water. In 2003, 2006 and 2009, the UN World Water Development Report was launched on the occasion of the World Water Day. The fourth Report is expected to be released around 22 March 2012.^{[citation needed]}

International observance (also known as international dedication or international anniversary) denotes a period of time to observe some issue of international interest or concern. This is used to commemorate, promote and mobilize for action. Many of these periods have been established by the United Nations General Assembly, Economic and Social Council or by UNESCO. In this case, the lead agency for a particular international observance uses the symbolism of the United Nations (UN) or UNESCO, a specially designed logo for the year, and their infrastructure to coordinate events worldwide. It also presents a written report about the event. This summarizes the activities that took place around the world under the auspices of the international observance, and makes recommendations for the future.

Below follows a list of consecutively days, years and decades that have been denoted as international observances by the United Nations. There are also other organizations that declare international observances but those are not as widely recognized.