“Rich and greedy” people in Melbourne and Sydney are overconsuming water on their pools and gardens, leaving poorer people without basic access, according to a new report.

Research has found social inequalities in cities are causing huge gaps in the urban water shortage crises as the wealthy over-pump supplies to keep their swimming pools clean and full, gardens watered and cars washed, while others lack basic means.

International researchers from Reading University in the UK, Sweden and the Netherlands found Melbourne and Sydney ranked among “the most severe” of its 19 large cities found to overuse water.

The study that focused on Cape Town found similar patterns in London, Miami, Barcelona, Beijing, Tokyo, Istanbul, Cairo, Moscow, Bangalore, Chennai, Jakarta, Maputo, Harare, Sao Paulo, Mexico City and Rome.

Lead researcher Elisa Savelli, from Uppsala University in Sweden, said the elite and upper-middle-income households consume “unsustainable” levels of water, while informal dwellers do not have taps, or toilets inside their premises.

“This is a wake-up call for Sydney and Melbourne, there are rich people in those cities that like to have barbecues, water their grand lawns and tend to their big pools – next summer if there is a drought in Australia these cities are going to be in trouble,” Ms Savelli said. “The increase in water crisis is not only due to climate change but also caused by the rich and greedy in Sydney as well as Melbourne because they are using water in an unsustainable way.

“They need to look at using water in a more homogeneous way to reduce the water crisis of the cities. Sydney and Melbourne are among the most severe cities where the elite overuse water.”

The report, released Tuesday, states in both the northern and the Southern hemispheres, found metropolitan areas experience extreme droughts and unsustainable levels of water consumption.

Professor Hannah Cloke, a hydrologist at the University of Reading who co-authored the study, said climate change and population growth mean water is becoming a more precious resource in big cities but research shows social inequality is to blame for poorer people not getting access to water for their daily needs.

“More than 80 big cities worldwide have suffered from water shortages due to droughts and unsustainable water use over the past 20 years, but our projections show this crisis could get worse still as the gap between the rich and the poor widens in many parts of the world,” Ms Cloke said.

The UK National Infrastructure Commission estimates four billion extra litres of water will be needed in England by 2050. Half of this will be met by increased supply, the government has said, with the other half coming from improving water efficiency, reducing demand, and cutting wasted water.

The current study was led by Dr Savelli of Uppsala university along with colleagues from the University of Reading, Vrije Universiteit Amsterdam, and the University of Manchester.

They analysed the domestic uses of water in Cape Town to understand the differences between social classes, separating them into five groups ranging from elite (people who live in spacious homes with large gardens and swimming pools) to informal dwellers (people who live in shacks on the outskirts). Elite and upper-middle-income households make up less than 14 per cent of Cape Town’s population but use more than half of the city’s water. Informal and lower-income households account for 62 per cent of the population but use just 27 per cent of the water.