A new study revealed over half the world's population — 4.4 billion people — cannot access safely managed drinking water, according to DW.
The numbers are double the 2022 Health Organization (WHO) estimate of 2.2 billion people.
But the report only examined access to clean water in low and middle-income countries, meaning the figure would likely be greater once poor access in higher income countries is accounted for. The numbers account two-thirds of those living in low and middle-income countries.
"The information which we have points towards very high rates of contamination," said lead researcher Esther Greenwood from ETH Zurich, Switzerland.
Drinking contaminated water has a risk of causing a variety of severe water-borne diseases like cholera, dysentery, typhoid, and less severe diseases like norovirus.
Water that is considered "safely managers" must be available on demand, on premises and contaminant-free, and designed to deliver safe water.
The research suggests that drinking water supplies are likely to be contaminated by fecal material in areas without access to water management services.
Greenwood's study was conducted to plug existing data gaps.
Satellite observations and household survey information were analyzed using artificial intelligence to define areas of safe and unsafe water access.
Greenwood says the findings are conservative as the data are samples taken on a single day rather than over extended timescales.
"It could actually be that the numbers are even higher," she said.
The analysis considered human and environmental impacts that limited safe water access across the UN's 22 geographic subregions.
It predicted 1.2 billion people living across India, Afghanistan, Bangladesh, Bhutan, Iran, the Maldives, Nepal, Pakistan and Sri Lanka — more than half of the region's population — were not using safe managed drinking water.
But South Asia fares better than others on a per capita basis.
More than 80% of people living in Sub-Saharan Africa, and around 75% in regions across Oceania (excluding Australia and New Zealand) and Southeast Asia cannot access safe managed water.
About half of these populations may be exposed to contaminated drinking water, according to the study.
The analysis used E.coli bacteria as a proxy indicator for contamination.
E.coli are associated with diarrhoea-related diseases and often result from exposure to contaminated food and water. While healthy adults usually experience mild symptoms and recover quickly, children and older people are at risk of developing kidney failure and death.
Greenwood said E.coli is "an indicator that there could have been recent fecal contamination." She adds that in feces there's a high risk of having other pathogens spread.
Water contaminated with E.coli caused a norovirus outbreak in Italy this summer, and caused several athletes to get sick after swimming in the River Seine during this year's Olympic games.
E.coli is not the only potential cause of water contamination. While not included in this study, arsenic and fluoride levels are also used to monitor chemical contamination in water.
A 2023 study estimated around 100 countries were affected by fluoride contamination in their groundwater.
The same researchers found 230 million people — mostly in Asia — were at risk of arsenic-contaminated groundwater contamination.
While contaminants can be naturally occurring — more than 80% of both fluoride and arsenic groundwater contamination is attributed to geological processes — industrial use of chemicals and coal burning can also contribute to water contamination.
"It seems that more households are affected by E.coli contamination than by chemical contamination. But I think that chemical contamination has different implications for people's health. It's something which would also need to be further investigated," Greenwood said.
People's access to safe drinking water is dependent on their local geographic, sociocultural, and economic situation as much as it is which country they live in.
People in poorer rural areas often have the the greatest difficulties in accessing clean water.
Almost 500 million people worldwide collect water from unprotected wells, rivers, ponds, and lakes, the WHO estimated in 2022.
Data also shows people living in towns and cities with low-incomes, or informal or illegal settlements, have less access to improved sources of drinking water compared to other residents.
Global trust in water safety is low, with another study showing 1 in 2 people believe their drinking water sources could cause serious harm if consumed.
"It's not enough to have water flowing through the taps. People need to trust their water," said study lead Sera Young, an anthropologist from Midwestern University, Illinois, US.
Young said that frequent and open-access water testing is needed to help people trust their water supply. Making water quality tests public and results easy to understand will allow people to test for contaminants themselves.
Improving water supply and management infrastructure will make drinking water safer according to the study.