Ancient groundwater: Why the water you're drinking may be thousands of years old

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INTRO: Communities that rely on the Colorado River are facing a water crisis. Lake Mead, the river’s largest reservoir, has fallen to levels not seen since it was created by the construction of the Hoover Dam roughly a century ago. Arizona and Nevada are facing their first-ever mandated water cuts, while water is being released from other reservoirs to keep the Colorado River’s hydropower plants running.

If even the mighty Colorado and its reservoirs are not immune to the heat and drought worsened by climate change, where will the West get its water? There’s one hidden answer: underground.

As rising temperatures and drought dry up rivers and melt mountain glaciers, people are increasingly dependent on the water under their feet. Groundwater resources currently supply drinking water to nearly half the world’s population and roughly 40% of water used for irrigation globally.

What many people don’t realize is how old – and how vulnerable – much of that water is. Most water stored underground has been there for decades, and much of it has sat for hundreds, thousands or even millions of years. Older groundwater tends to reside deep underground, where it is less easily affected by surface conditions such as drought and pollution.

As shallower wells dry out under the pressure of urban development, population growth and climate change, old groundwater is becoming increasingly important.

If you bit into a piece of bread that was 1,000 years old, you’d probably notice.

Water that has been underground for a thousand years can taste different, too. It leaches natural chemicals from the surrounding rock, changing its mineral content. Some natural contaminants linked to groundwater age – like mood-boosting lithium – can have positive effects. Other contaminants, like iron and manganese, can be troublesome.

Older groundwater is also sometimes too salty to drink without expensive treatment. This problem can be worse near the coasts: Overpumping creates space that can draw seawater into aquifers and contaminate drinking supplies.

Ancient groundwater can take thousands of years to replenish naturally. And, as California saw during its 2011-2017 drought, natural underground storage spaces compress as they empty, so they can’t refill to their previous capacity. This compaction in turn causes the land above to crack, buckle and sink.

Yet people today are drilling deeper wells in the West as droughts deplete surface water and farms rely more heavily on groundwater... (MORE)

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