Longyearbyen tap water has been declared unsafe, and the town's 2,600 inhabitants are under an instruction not to drink what comes out of the pipes. Scientists trace the heavy metal contamination to thawing permafrost, and the ban first issued in September last year still stands.

A drinking ban in the Arctic's fastest-warming town

The order came from the municipality, Longyearbyen lokalstyre, which alerted residents in September last year after manganese in the supply reached 25 times the 50 micrograms per litre recommended by the Norwegian Institute of Public Health. The town draws its main drinking water from Isdammen, a dammed lake 2.5 km (1.5 miles) long whose name means "ice pond".

The setting matters:

• •Longyearbyen lies 800 miles from the north pole
• •It is warming five to seven times faster than the global average
• •Autumn temperatures there are rising by up to 4C a decade

Thawing permafrost and fool's gold

Climate-driven thaw has exposed bedrock that leaches metals into the lake. Researchers point to two factors: the thawing of permafrost and the geology of a former mining town.

Marjolaine Verret, a permafrost expert and associate professor in Arctic geology at the University Centre in Svalbard, said: "The combination of the thawing permafrost and the shale bedrock, which contains a mineral called pyrite, or fool's gold, is causing contamination". Pyrite oxidises when it meets water and oxygen, generating acidity that leaches heavy metals from the rocks into waterways; the local contaminant is manganese, though others can also be released.

Manganese, nickel and the mayor's view

Prolonged exposure to high manganese levels can cause neurological problems, particularly in children and infants. Mayor Terje Aunevik said drinking water quality had never been good because of sediment, but the manganese levels had "gone ballistic". He added that the levels were "not dangerous" but that government guidelines had to be followed, and acknowledged the crisis had created "noise" with some residents angry at the inconvenience.

Emergency measures and possible fixes

Since the ban, the town has set up a central tank of free purified water, filtered by the local brewery, where residents refill containers at the local supermarket, alongside an investigation into water quality. Manganese levels have since dropped, but earlier this year sulphate and nickel exceeded recommended drinking water limits, so the ban remains in place.

Aunevik has commissioned the investigation and said a "completely new water mains supply" may be needed. The options on the table include:

• •Installing a filtration system at Isdammen
• •Having a desalination plant as a backup, or the reverse

Either route would be "extremely expensive" and technically challenging, since water temperatures in Svalbard are often below zero. Aunevik noted how hard it is in Norway, where people take tap water for granted, to have to carry water, and urged other small communities to be precautious and think about what to do if it happens to their sources.

Verret and other scientists warn the contamination could be a first example of how climate change can impact freshwater, with pyrite-rich bedrock and thawing permafrost also found in northern Canada and Alaska.