Some 650 million people, or one in 10 of the world's population, do not have access to safe water, putting them at risk of infectious diseases and premature death.
Dirty water and poor sanitation can cause severe diarrheal diseases in children, killing 900 under-fives a day across the world, according to United Nations estimates - or one child every two minutes.
Among newborn babies, the World Health Organization says infections caused by a lack of safe water and an unclean environment cause one death every minute somewhere in the world.
The U.N. says access to safe drinking water and adequate sanitation services is vital to human health. It is also important for other reasons - ranging from easily identifiable and quantifiable benefits such as cost and time savings, to more intangible factors like convenience, well-being, dignity, privacy and safety.
The WHO estimates that every $1 invested in improving water supply and sanitation services yields gains of $4 to $12, depending on the type of intervention.
This year's United Nations World Water Day, marked on March 22, is focused on water and jobs and designed to highlight how water can create paid and decent work and contribute to a greener economy and sustainable development.