The world’s drinking water faces a new threat, with the largest study of its kind finding that climate change and increasing urbanisation are contaminating the aquifers that sustain more than half of the world’s population.

A study led by researchers at the University of New South Wales (UNSW) found that dissolved organic carbon (DOC) – a naturally occurring component of groundwater that is safe in small doses – will become elevated in aquifers in 32 countries across six continents, impacting potability, affordability and human health.

“We identified groundwater DOC concentration increases of up to 45%, largely because of increased temperatures in the wettest quarter of the year,” said lead author Dr Liza McDonough, of the Connected Waters Initiative Research Centre at UNSW.

“An increase in groundwater DOC concentration impacts the ability and therefore cost to make groundwater drinkable.”

In a report published in science journal Nature, the scientists said that while DOC occurs naturally, the problem lies in the elements of groundwater it could combine with and transport, including potentially dangerous heavy metals otherwise bound to rocks and sediment at the groundwater sites.

“This is a concern when, for example, more than 100,000 lifetime cancer cases in the United States (US) alone can be attributed to drinking water contaminants,” McDonough said.

The report noted that much of the risk identified is associated with the presence of disinfection by-products and arsenic.

While a number of recent studies have focused on the changing quantities of groundwater, the UNSW-led study emphasised the key drivers of water quality.

The report found that our “increasing reliance on groundwater due to climate change” may be compounded by both increased urbanisation and global population growth, which in turn may increase contamination.

Not only is the contamination a threat to drinking water supplies affecting millions of people, but researchers say that it is one that does not even fall under the oversight of water regulators.

“Because most health impacts caused by DOC are related to the formation of by-products of water treatment chlorination and depend on concentrations of other water chemical parameters, the World Health Organization and many countries – including Australia – do not regulate DOC concentrations in drinking water directly,” McDonough added.

In affected areas such as the south-east of the US, the report projected a 16% increase in annual household water costs. This is because of rising water treatment costs to remove increased DOC concentrations, which amounts to US$134 [AUD$222] for a family of four per year.

Critically for Australia, where groundwater is widely used as the main source of drinking water for many urban areas, the problem is magnified in arid conditions.

The researchers found that rainfall in humid environments dilutes the DOC concentration in groundwater, while there was a “significant increase of 19% in groundwater DOC concentrations in urban areas compared to natural land”.

The report concluded that contamination will be a particularly significant issue for regions with a large or increasing reliance on groundwater as a source of freshwater.

With even relatively small DOC increases in raw groundwater impacting health and the cost of water treatment, the researchers are now turning their focus to finding a solution.

“Our next step is to investigate how the character of DOC changes when you have different aquifer minerals, because some types of organic matter can stick to certain mineral surfaces and ultimately reduce this type of organic matter remaining in the water,” McDonough said.

“This will help provide guidance on the most suitable water treatment options in areas where DOC concentrations are expected to increase.”

Originally published by Water Source, 20 March 2020.