Millions of people around the world continue to be at risk from the drinking of contaminated water, the United Nations Children’s Fund (UNICEF) warned on Tuesday in a statement issued as part of events to mark the World Water Day. UNICEF said the push to bring safe water to millions around the world is going to be even more challenging due to climate change, which threatens both water supply and water safety for millions of children living in drought- or flood-prone areas.

In 2015 at the end of the Millennium Development Goal era, all but 663 million people around the world had drinking water from improved sources – which are supposed to separate water from contact with excreta. However, data from newly available testing technology show that an estimated 1.8 billion people may be drinking water contaminated by e-coli – meaning there is faecal material in their water, even from some improved sources.

“Now that we can test water more cheaply and efficiently than we were able to do when the MDGs were set, we are coming to terms with the magnitude of the challenge facing the world when it comes to clean water,” said Sanjay Wijeserkera, head of UNICEF’s global water, sanitation and hygiene programmes. “With the new Sustainable Development Goals calling for ‘safe’ water for everyone, we’re not starting from where the MDGs left off; it is a whole new ball game.”

One of the principal contributors to faecal contamination of water is poor sanitation. Globally 2.4 billion people lack proper toilets and just under 1 billion of them defecate in the open. This means faeces can be so pervasive in many countries and communities that even some improved water sources become contaminated.

The safety concerns are rising due to climate change.

When water becomes scarce during droughts, populations resort to unsafe surface water. At the other end of the scale, floods damage water and sewage treatment facilities, and spread faeces around, very often leading to an increase in water-borne diseases such as cholera and diarrhoea.

Higher temperatures brought on by climate change are also set to increase the incidence of water-linked diseases like malaria, dengue – and now Zika – as mosquito populations rise and their geographic reach expands.

According to UNICEF, most vulnerable are the nearly 160 million children under 5 years old globally who live in areas at high risk of drought. Around half a billion live in flood zones. Most of them live in sub-Saharan Africa and in Asia.

Starting on World Water Day and ending with the signing of the Paris Agreement on April 22, UNICEF is launching a global Instagram campaign to raise awareness of the link between water, the environment, and climate change.

Using the #ClimateChain hashtag, UNICEF Executive Director Anthony Lake, UN General Assembly President Mogens Lykketoft, UN climate chief Christiana Figueres, and other prominent figures will figuratively join hands with members of the public in a chain of photographs intended to urge action to address climate change. The images will be presented at the signing of the Paris Agreement.

UNICEF is also responding to the challenges of climate change by focusing on disaster risk reduction for water supplies. In a recent publication, ‘Unless We Act Now’, UNICEF set out a 10-point climate agenda for children. It sets out concrete steps for governments, the private sector and ordinary people to take in order to safeguard children’s futures and their rights.