STOCKHOLM, June 9 (Xinhua) -- Groundwater levels are sinking fast in parts of Sweden, endangering the supply of clean water from wells and waterworks amid an enduring heat wave in the Scandinavian nation, Swedish Television reported on Saturday.

"While the municipal water supply should not be under threat, there are local deviations," said Bo Thunholm of the Geological Survey of Sweden, which is responsible for monitoring groundwater levels across the country.

Some groundwater storages in southern and central Sweden are now nearing record-low levels. According to the Geological Survey of Sweden, levels in some smaller storages have not been this low since 1968, which is when the Geological Survey of Sweden started monitoring the groundwater supply.

Around a million residents, in both permanent and temporary dwellings, access drinking water from private wells and that is where the situation is most critical.

The latest measurement was carried out in the middle of last month. But as the heat wave has continued since then, the groundwater levels today have also further dropped.

"Even if the situation is not critical," Thunholm said, "one should be vigilant and exercise caution".