Approximately 1.42 million people are scattered throughout the islands of Hawaii, and every single one of them needs potable water to drink. As do the animals living here, the plants growing here, the insects crawling through the vegetation, and the birds singing in the branches. Everything needs fresh water for life.

Once upon a time, when the population of Hawaii was smaller, it was easier for nature to supply the needs of the islands. Fresh water was considered sacred, so the people used only as much of it as was absolutely necessary. The water, wai, was shared equally, because the Hawaiians believed that all land and water belonged to the gods. The Hawaiian word for law, kānāwai, is translated as an equal sharing of water. Fresh water was, and is, so valuable that Hawaiians use waiwai as an expression of wealth.

All of Hawaii’s potable water comes from its rain. Experts believe that on average, every day, about 1.8 billion gallons of rain water falls on Oahu alone. It’s estimated that about one third of that amount runs off, and another third is absorbed by plants, or evaporates. Luckily, about a third of the rain water soaks in, recharging the groundwater, which in turn replenishes the aquifer. But water can take anywhere from one to 25 years to reach an aquifer, and when it does, the water is not simply filling an underground hole. An aquifer is composed of saturated rock. Of course, in Hawaii, the rock is porous lava that has slowly been infiltrated by rain water over many years.

Recently, though, a very different kind of aquifer was discovered by a scientist with a hunch. Studies of aquifers on the big island of Hawaii revealed that they were leaking heavily. The conventional thinking was that the water was seeping out at the coastline, or traveling laterally along the island.

It took a postdoctoral researcher at the University of Hawaii to prove that there are underground rivers of fresh water flowing as far as 2-1/2 miles out into the ocean. Working with the Scripps Institute of Oceanography, Hawaii’s Dr. Eric Attias used electromagnetic imaging to prove that his thinking was correct.

Electromagnetic equipment was towed over submerged rocks near Hualalai volcano. Because saltwater conducts electricity better than fresh water, the scans mapped where the fresh water flowed. The electromagnetic image showed underground rivers of fresh water running through fractured volcanic rock. The fresh water rocks are, of course, surrounded by porous rock saturated with salt water, but thin layers of an impermeable rock, formed by compacted ash and soil, appear to keep the two kinds of water separate.

The discovery was made over 2 years ago, and immediately, there was excitement about pumping fresh water from these previously unknown aquifers. Some others took a more cautious approach. One hydrogeologist pointed out that because the newly found fresh water is part of the entire aquifer system, draining the new water could adversely impact the ecosystem on the big island.

A treasure has been found. Use it, or guard it, or study it further? The discussion continues.