The World Health Organization has warned that nearly two billion people worldwide currently use faecal-contaminated water.
The UN agency says dramatic improvements are needed in ensuring global access to clean water and sanitation.
The WHO says hundreds of thousands of people die each year because they are forced to drink contaminated water.
It is urging large investments to help provide universal access to safe drinking water.
"Today, almost two billion people use a source of drinking-water contaminated with faeces, putting them at risk of contracting cholera, dysentery, typhoid and polio," Maria Neira, who heads WHO's public health department, said in a statement.
"Contaminated drinking-water is estimated to cause more than 500,000 diarrhoeal deaths each year and is a major factor in several neglected tropical diseases, including intestinal worms, schistosomiasis and trachoma," she added.
The report welcomed the fact that countries had on average raised their annual budgets for water, sanitation and hygiene by 4.9% over the past three years.
But it says 80% of countries acknowledge that their financing is still not enough to meet their nationally-set targets for increasing access to safe water and sanitation.
"In many developing countries, current national coverage targets are based on achieving access to basic infrastructure, which may not always provide continuously safe and reliable services," the WHO warned in a statement.
Guy Ryder, Chair of UN-Water and head of the International Labour Organization, said "increased investments in water and sanitation can yield substantial benefits for human health and development, generate employment and make sure that we leave no one behind".