We’ve long been taught not to take Hawaii’s fresh water resources for granted.

The Board of Water Supply reminds us to conserve water, especially in the hot, dry summer months. Taro farmers on Maui have fought long legal battles to restore diverted water to the streams that feed their lo‘i. Population growth and new housing developments spur concerns that they will drain groundwater aquifers faster than they can be replenished.

Now comes some assumption-altering news. A University of Hawaii study released this week reports that researchers using an electromagnetic imaging technique have found evidence of a vast reservoir of fresh water off Hawaii island — double the amount previously thought.

The findings, published in the journal Science Advances, show a newly discovered kind of plumbing system that could exist on other volcanic islands — what UH called “a novel way in which substantial volumes of freshwater are transported from onshore to offshore submarine aquifers.”

The study described how large amounts of groundwater flow through fractured basalt to the ocean, separated from seawater by a thin low-permeability layer.

Brian Taylor, UH-Manoa School of Ocean and Earth Science and Technology (SOEST), said in a university press release that the evidence for separate freshwater lenses, one above the other off the Kona coast, “profoundly improves the prospects for sustainable development on volcanic islands.”

That would be good news for people living with water shortages in places like Hawaii, including densely populated Oahu. Ranchers and farmers struggling with drought conditions could hope for some relief. It also could change the thinking on how the state’s water resources should be managed. Researchers say that tapping these new sources of fresh water would be less expensive than other options, like desalination.

It’s a rare thing to learn about a previously unknown abundance of a resource as precious as fresh water. Still, that does not negate the value of managing it conservatively, especially in this time of uncontrolled climate change. Abundance encourages wastefuless, as we have seen, for example, in the ruthless depredation of rain forests and Atlantic bluefin tuna.

When it comes to Hawaii’s fresh water, the mantra should continue to be one of sustainability: “Waste not, want not.”