There is no doubt that climate change is impacting Pacific island nations harder than most – and sooner than most, too. Surprisingly, archaeologists have discovered that some islanders have been coping with climate issues for hundreds of years. By Jeremy Torr.

Rapa Nui, Chile. October 2021. “For all the Pacific islands, climate change is going to dramatically impact the availability of fresh water, from increasing sea levels to storm surges and less predictable rainfall patterns.” So says Prof. Robert DiNapoli, from the environmental studies and anthropology department at Binghamton University, New York. But although it’s in the news, drinking water scarcity on Pacific islands is not a new problem.

When the first European explorer Jacob Roggeveen, chanced across what is now known as Easter Island (or Rapa Nui) back in 1722, he was prompted to note in his ship’s log (as well as the huge stone heads dotted everywhere) that thirsty natives seemed to quite happily drink seawater.

One of the reasons, he observed, was that there was virtually no freshwater on the tiny remote island, more than 1600km from the nearest island and over 3500km from the coast of Chile. Just a couple of small, frequently dry, crater lakes and a small marshy area. But even so, drinking seawater? Surely not! Well, yes and no.

The explanation is complex. The substrata of Easter Island is permeable (porous) rock, mostly composed of a multilayer accumulation of latticed, layered basalts alternating with low-permeability layers of dense volcanic ash or soil. This means what little water that does fall as rain or condensed sea mists simply vanishes into the water permeable rock, making it very hard to catch and store – unlike places with impermeable soils and river systems. But the key to those seawater drinking natives lies in the way the water disappears into the ground.

As it soaks into the permeable layers, it eventually hits the waterproof ash/soil layers. The only thing the water can do then is to slither sideways, across the island, underground, and dribble out of the permeable basalt layers into the sea at what they called seeps. As the layers generally slope down towards the edge of the island, a lot of these coastal freshwater seeps were below sea level.

And this is where the seawater-drinking natives come in. Because freshwater is slightly less dense than seawater (it has no salt in it) it floats on top of the sea. So the freshwater that oozed out into the sea floated to the top. And the canny, thirsty natives sipped only the top bit of sea, and got fresh water, not brine. Simple.

But as anybody that has had a Radox bath will know, fresh water mixes with salty quite easily.

So those smart Rapa Nuians built little underwater dams or “ponds” just offshore to keep fresh and seawater separated and provide reliable drinking water sources. Sure, they had to be careful they didn’t dip their buckets too deep into the water or they would get a whole lot of salt, but as long as they just skimmed the top layer, it was freshwater for tea.

Using drones, DiNapoli and his team worked out exactly how and where the first inhabitants had used simple water engineering to survive droughts on their remote homeland. As he notes, the way they approached what was a serious problem can possibly be used on future solutions to island water shortages, drought and drought prevention.

"They were faced with a very difficult place to live,” says Dinapoli. “But they came up with these (viable) strategies for survival. (Rapa Nui) provides an interesting example of how its people responded to the constraints of their environment.”

“This (technology) reflected generations of cultural (living) centred on water, but also on … the island's precarious sustainability. Despite limitations, the islanders succeeded by sharing activities, knowledge, and (restricted) resources for over 500 years until European contact.”

 Definitely something to learn from.