While residents of Cape Town, South Africa, brace for Day Zero (the day that the city of 4 million’s municipal water supply will be cut off for most households and businesses in order to preserve water after a severe drought that has emptied reservoirs), they are far from alone.

As MarketWatch’s Ciar Linnane notes, experts say this dystopian scene could be played out in other major cities in the coming years, as demand for water continues to increase with population growth and as climate change makes already-dry regions still dryer.

More than 5 billion people could suffer water shortages by 2050 due to climate change, increased demand and polluted supplies, according to a UN report on the state of the world’s water.

As The Guardian reports, the comprehensive annual study warns of conflict and civilisational threats unless actions are taken to reduce the stress on rivers, lakes, aquifers, wetlands and reservoirs.

Demand for water is projected to rise fastest in developing countries. Meanwhile, climate change will put an added stress on supplies because it will make wet regions wetter and dry regions drier.

“For too long, the world has turned first to human-built, or ‘grey’, infrastructure to improve water management. In doing so, it has often brushed aside traditional and indigenous knowledge that embraces greener approaches,” says Gilbert Houngbo, the chair of UN Water, in the preface of the 100-page assessment.

“In the face of accelerated consumption, increasing environmental degradation and the multi-faceted impacts of climate change, we clearly need new ways of manage competing demands on our freshwater resources.”

By 2050, the report predicts, between 4.8 billion and 5.7 billion people will live in areas that are water-scarce for at least one month each year, up from 3.6 billion today, while the number of people at risk of floods will increase to 1.6 billion, from 1.2 billion.

Water quality is also deteriorating.