Water contaminated with toxic metals is killing millions of people globally every year, a study suggests — and the majority of Americans drink it.

Researchers at the World Bank claim that lead in drinking water is responsible for more heart disease than smoking or bad diets.

Using blood tests from thousands of adults in 183 countries, they simulated the number of deaths from heart disease caused by lead — with their model saying 5.5million were caused by the heavy metal.

For comparison, smoking was linked to two million deaths from heart disease worldwide, while high cholesterol contributes to 2.6million.

Researchers based in Washington D.C. said their study was a 'wake-up call' to get lead out of the water supply, with 56 percent of Americans still drinking water contaminated with the heavy metal.

Heart disease is the leading cause of death globally, behind an estimated 8.9million deaths in 2019 alone.

It is also the leading cause of death in the US, according to the Centers for Disease Control and Prevention (CDC), behind 695,000 deaths per year.

Lead is an extremely toxic heavy metal that can accumulate in the body over time leading to a range of heart problems.