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Water in Philippine City Safe to Drink, Study Using Isotopic Techniques Finds

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Isotopic techniques have confirmed that the city water in the water tanks behind these boys, and on many streets in new neighbourhoods in Tacloban, is safe to drink. (Photo: M. Gaspar/IAEA)

Tacloban, Philippines – The drinking water of this city of 250,000 is safe, is getting regularly recharged and is not under threat by the sea. Sounds simple? This conclusion took years of research and the analysis of thousands of water samples to establish, and required the use of isotopic techniques by researchers from the Philippine Nuclear Research Institute (PNRI), with support from the IAEA and the Food and Agriculture Organization of the United Nations (FAO).

When a storm surge caused by Typhoon Haiyan, the strongest tropical storm in the world, devastated much of this city and killed thousands in 2013, local authorities faced the daunting task of reconstruction, including moving people away from the most flood-prone areas. But could the waves that swept away buildings and people have reached the city’s water reservoir?

There was a danger that the storm surge could have contaminated the aquifer – an underground layer of permeable rock containing groundwater – the city’s major water source. Salt and other flood-borne contaminants, including organic matter from animal and human corpses, could have rendered the water unfit for consumption. PRNI turned to the IAEA technical cooperation programme for assistance in the use of isotopic techniques to characterize the aquifer.

Not all water molecules are created equal

While all water molecules consist of an oxygen and two hydrogen atoms, a small percentage of these atoms have extra neutrons in their nucleus. Exactly what percentage depends on the age and source of the water. Therefore, an analysis of the isotopic makeup of the groundwater enables researchers to find out whether the aquifer is getting recharged, i.e. receiving a regular dose of “new” water from rain.

The scientists set up 32 monitoring stations for groundwater and used both conventional and nuclear techniques for the characterization of the water. They found very little sodium and chloride – thereby concluding that seawater did not enter the aquifer. They also found that the isotopic composition of the water in the aquifer is close to that of today’s rainwater – which meant that the city’s water supply was not in danger of disappearing, explained Raymond Sucgang, a senior researcher with PNRI who led the project. “Tacloban is a growing city with a growing economy, so it is comforting to know that its groundwater is getting replenished from rain,” he said.

The concentration of nitrogen and organic matter in the water is very low – which indicates that no biological contamination occurred. “These potential contaminants probably decayed before they could get to the groundwater,” Sucgang said.

The next step in the project is for PRNI to determine the exact rate of water recharge, and based on that make policy recommendations to the local government for the protection of the city’s water supply, Sucgang said. “It’s good to know that there is no immediate danger, but policy for sustainable water use is still required,” he added.

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