U.S. groundwater continues to go dry based on humanity’s seemingly insatiable desire to drink and grow food. Who'd a thunk? People need to eat. Eating requires water. As populations increase, more food is needed, meaning more water is needed.

Alternatively, any livestock grown for consumption needs water, too. The best place to get the water? From the ground.

According to a recent study published in the journal Nature, water stored in aquifers underground makes up the vast majority of accessible freshwater on Earth. Its abundance has fueled forays into drier locales, enabling a boom in crop production.

People and livestock are not the only things relying on aquifers. While about 70% of all groundwater used worldwide goes to agriculture, surface waterways, including rivers and streams, need groundwater, too. As groundwater gets pumped to Earth too quickly, these water arteries diminish, too.

The Nature study shows the water is at an “ecological tipping point” that scientists call the “environmental flow limit.” Environmental flows are the quantity, timing, and quality of water flow required to sustain freshwater and estuarine ecosystems and the human livelihoods and well-being that depend on these ecosystems.

This limit has been reached in 15% to 21% of watersheds tapped by humans. The majority of these resources are in drier regions like parts of Mexico and northern India, where groundwater is used for irrigation. At this rate, in about 30 years — by 2050 — the study authors note that anywhere from 42% to 79% of pumped watersheds will have crossed this threshold.

“Already, unsustainable groundwater pumping exceeds recharge from precipitation and rivers, leading to substantial drops in the levels of groundwater and losses of groundwater from its storage, especially in intensively irrigated regions,” the study’s authors note.

“When groundwater levels drop, discharges from groundwater to streams decline, reverse in direction or even stop completely, thereby decreasing streamflow, with potentially devastating effects on aquatic ecosystems.”

According to the American Geosciences Institute, groundwater is any water found underground in the cracks and pores in soil, sand, or rock. Groundwater is replenished almost entirely by rainfall. In the United States, roughly one-quarter of all rainfall becomes groundwater. Groundwater makes up approximately 90% of the total available freshwater in the United States.

In many areas, groundwater use outpaces groundwater recharge. “Groundwater is replenished when rainfall soaks into the ground, but it can take hundreds to thousands of years to replace what we extract,” the institute said. “In arid areas, high demand for groundwater and slow replenishment provide challenges for sustainable groundwater management.”

A healthy aquifer ecosystem protects against seasonal fluctuations in water availability, providing stability for resident plants and animals. “But if too much groundwater is pumped, surface waters begin to seep into the aquifer, draining the life from many river and stream habitats,” the institute notes.

Irrigation provides about 80% of freshwater consumption. Annually, groundwater provides 43% of the freshwater used for irrigation. Groundwater accounts for around 40% of U.S. freshwater consumption, and is not easily, nor quickly, replaced.