The temples and towers of the 400-square-kilometre Angkor site sit on a base of sand, kept firm by a constant supply of groundwater that rises and falls with the seasons, but which is now being used to supply a burgeoning city.
With the number of visitors approaching 2 million a year, increasing pressure is being put on the scarce water resource. Thousands of illegal private pumps have been sunk across the city, pulling millions of litres of water from the ground each day.
UNESCO, the cultural arm of the United Nations, says that no one knows just how much water is being drawn from the ground, or how much can be taken safely.
Water is a precious commodity in Siem Reap, particularly during the dry season, when tourist numbers are highest. And the population of the city, barely five kilometres from Angkor Wat, has doubled in a little more than a decade to about 200,000.