Archaeologists have figured out a lot about the moai, the giant stone heads found on Rapa Nui or Easter Island, a tiny dot of land in the Pacific Ocean administered by Chile. They know what quarries the stone came from, how they were transported across the island and even how they got their distinctive hats. But one big mystery has remained—why exactly were the giant statues placed in certain spots around the island?

One group of researchers believes they have an answer. Nicola Davis at The Guardian reports archaeologists theorize the location and size of the moai and the monumental raised platforms many of them sit on, called ahu, indicate the presence of fresh water on the island, which has no above ground streams or rivers flowing across it.

The theory emerged when the researchers used spatial modeling to explore the relationship between the locations of 93 of the ahu on the eastern half of the island and available resources. The team looked at the location of marine resources, mulched gardens where crops like sweet potatoes were grown and water resources including wells and seeps where drinkable but brackish freshwater flows out of the ground near the coast at low tide. The study appears in the journal PLOS One.

Wherever water seeped out of the coast, the team found platforms for statues. And in areas in the interior where there were platforms but didn't seem to be any water, they found the remains of ancient wells that tapped the islands underground aquifers. The size of the statues seemed to correspond to the amount of water available as well. In areas with no water resources, there were no moai or ahu. “Every time we saw massive amounts of fresh water, we saw giant statues,” co-author Carl Lipo from Binghamton University tells Davis. “It was ridiculously predictable.”

The study also contradicts the long-held idea that the inhabitants of the island suffered an ecological collapse that led to warfare between various bands and intense competition to build the statues that led to the society’s collapse. Instead, recent research indicates the inhabitants of the island were cooperative, both in the construction of the moai, which likely represented ancestors, and in sharing resources like water.

“In this way, the monuments and statues of the islanders’ deified ancestors reflect generations of sharing, perhaps on a daily basis—centered on water, but also food, family and social ties, as well as cultural lore that reinforced knowledge of the island's precarious sustainability,” co-author Terry Hunt of the University of Arizona says in a press release. “And the sharing points to a critical part of explaining the island's paradox: despite limited resources, the islanders succeeded by sharing in activities, knowledge, and resources for over 500 years until European contact disrupted life with foreign diseases, slave trading, and other misfortunes of colonial interests.”

But not everyone thinks the new spatial analysis explains the positioning of the ahu. Jo Anne Val Tilburg, an Easter Island researcher from the University of California, Los Angeles, tells Davis at The Guardian that the coastal water seeps were a minor resource and it’s highly unlikely the islanders would have built such massive constructions to mark them.

Even if the statues aren’t related to the availability of water, they are beginning to tell a tale much different from the one spun in the past decades, most notably in Jared Diamond's popular book Collapse. It’s believed when Polynesians reached Rapa Nui around 1200 A.D. it was covered with palm trees. But the settlers brought with them non-native rats, which multiplied and ate tree seedlings, meaning the island's forests could not renew themselves. In the face of a changing environment the islanders did not descend into warfare, genocide and cannibalism, but instead adapted to the new situation, eating lots of rats, drinking brackish water and cooperating with one another to make giant statues that still amaze people around the world over 800 years later.