WHAT IS GROUNDWATER DEPLETION?

Groundwater – it’s (probably) what’s in your cup! Drinking water comes from lakes, rivers, and streams, or it comes from groundwater, which is water underneath the Earth tucked away in the soil, sand, and porous rock. A large amount of groundwater in one place is called an aquifer.

According to the U.S. Geological Survey, 68% of freshwater on the planet is frozen in ice caps, glaciers, and permanent snow. Less than 1% of freshwater flows through lakes and rivers, and the remaining 30% of freshwater in the ground.

Groundwater depletion is pretty straightforward. When people draw water from an aquifer faster than nature can replenish water through rain and other means, the aquifer slowly drains and can eventually run out of groundwater.

Groundwater depletion poses a massive problem for the surrounding area. If your city runs out of water, that’s game over! You would need to pack up and move somewhere with accessible drinking water, or the government would have to pay a pretty penny to ship water from somewhere else.

WHY HAS GROUNDWATER USE INCREASED?

51% of the U.S. population relies on groundwater, according to the Groundwater Foundation. So why is it slipping away?

As the BBC reported above, the population keeps climbing, and growing cities need water for manufacturing and agriculture. The BBC report also notes that climate change is aggravating water scarcity. Increased frequency and intensity of droughts and floods affect the water supply along with rapid glacial melting that can raise the sea level and lead to saltwater intrusion (what is saltwater intrusion, you ask…we’ll cover it in just a few paragraphs).

Fossil water, a type of paleowater, has been in the ground for millennia and can’t can’t replenish naturally, according to World Atlas. An area may not be able to replace fossil water because the water entered the aquifer under geological conditions that differ from those of the present.

In regions where precipitation is low, aquifers receive little-to-no recharge and are considered a non-renewable resource. We can’t replace fossil water, but municipalities may come to rely on this water to keep up with demand.

EFFECTS OF GROUNDWATER DEPLETION

Here’s what can happen when we keep slurping up groundwater:

• Ground subsistence – Have you ever watched a terrifying video where the ground seems to collapse in on itself? The culprit might be ground subsistence. Water in an aquifer often acts as structural support. Once it’s gone, the ground can compact. Beyond the obvious danger, ground subsistence means that the aquifer’s ability to hold water is reduced because the soil was compacted, as reported by Clean Technica.
• Lowered water table – Imagine you’re drinking a milkshake. As you drink, the top goes down, yes? When we drain groundwater, the water table, or the top of the aquifer, moves further into the ground. As the USGS notes, lowered water tables can cut off well access. Well owners might need to dig another well entirely to access their water.
• Reduced water quality – The same USGS page above also explains that water quality can deteriorate as water levels in an aquifer drop. Rising levels of salinity can affect lowered aquifers. One of the primary causes of this phenomenon is saltwater intrusion.
  

WHAT IS SALTWATER INTRUSION?

Saltwater intrusion is the other heavy hitter in the realm of groundwater depletion.

You don’t need a degree in chemistry to know that you shouldn’t drink saltwater. Unfortunately, as the planet heats up, the sea levels rise, and saltwater is creeping even further in from the coastline, threatening our water supplies.

Here’s a quick breakdown of saltwater intrusion, courtesy of the USGS: when flood water or ocean water reaches the land, it can encroach into aquifers depleted of groundwater. Once the saltwater and freshwater mix, there’s no separating the two. That aquifer is compromised.

According to that USGS page, states that are the most at-risk for saltwater intrusion are coastal states, such as Florida. Freshwater levels have decreased compared to the sea level, which allows a higher gradient of water to flow toward the freshwater.

HOW DOES SALTWATER INTRUSION OCCUR?

According to that USGS page, states that are the most at-risk for saltwater intrusion are coastal states, such as Florida. Freshwater levels have decreased compared to the sea level, which allows a higher gradient of water to flow toward the freshwater.

How does saltwater intrusion occur?

Great question! Under normal conditions, the natural barriers between freshwater and saltwater are pretty reliable. But, as we continue to pump groundwater out of aquifers, saltwater can migrate inward and upward to take up the vacant space, according to a report in Circle of Blue. If you want a brief introduction to the phenomenon of osmosis, check out our guide to reverse osmosis.

Obviously, this can cause a huge headache for coastal communities. According to the Groundwater Association, a cone of depression can form in the water table under a well. This process sucks saltwater into an upright cone below the well, and, if the rate of pumping increases, the saltwater cone can breach the well.

This all sounds pretty bleak. What can we do about it?