Cities of the world are under threat because of water quality issues, United Nations Habitat says.

"The fact of the matter is that our cities in the world are under threat. Johannesburg is one of those cities," said UN Habitat spokesman Piers Cross.

Regardless of Johannesburg's water problems, it was probably one of the easiest to solve when compared to some other countries, he said.

Cross was speaking in Rosebank, at the announcement of World Water Day celebrations in Cape Town from March 20 to 22 by the water affairs department, UN Habitat and the African Ministers Council of Water.

"The water quality issue is not just an isolated thing, most cities around the world are facing huge environmental problems in their water development and their management of waste," he said.

He used the example of the cholera outbreak in Harare in 2009 where 100,000 people were infected "because there wasn't sufficient investment and management in sanitation services."

Cross said it was important to learn and compare how other countries were handling these issues.

"What's important to recognise is that the pollution questions are a global problem, it's not just Johannesburg that has this problem."