For a planet where water covers 70 percent of the surface, Earth certainly makes its residents work hard for a drink. Aside from fish and other saltwater-sipping sea life, most of us have to share what little freshwater we can find on land.
And that's no small task. Only 3 percent of all water on Earth is freshwater, more than two-thirds of which is locked up in glaciers and ice caps. Of the other third, barely a trickle collects on the surface — lakes, rivers, streams and swamps represent less than 0.5 percent of all freshwater worldwide.
So where's the rest of it? An estimated 2.5 million cubic miles of freshwater are neither frozen, floating nor flowing on the surface, yet they account for at least 30 percent of total freshwater on the planet. Don't bother looking on the planet for all that water, though; it's actually in the planet. And while such a hidden location usually makes this underground ocean of freshwater safer to drink, it can also make it more dangerous — something the EPA recently acknowledged when it announced plans to crack down on the country's biggest water polluters.
What is groundwater?
Groundwater is simply water — mainly from rain and snow, but also from some human activities — that has soaked into the soil. That's the end of its journey from our perspective, but the water keeps going long after it's gone underground. It percolates downward, with dirt and rock particles filtering out dangerous bacteria as it sinks. When it finally reaches an impermeable layer of bedrock deep below the surface, it stops and begins to saturate the surrounding soil. Over many millennia, this pool of purified groundwater can grow into vast subterranean aquifers.
Some groundwater may eventually become encased in rock thanks to gradual geologic shifting, forming pressurized pockets known as "confined aquifers." These require complex drilling and pumping operations to extract their contents, leaving such deep deposits mainly for industrial uses such as large-scale farm irrigation. Other groundwater deposits are limited only by water supply and the bedrock below, and these "unconfined aquifers" make up the majority of residential groundwater sources in the United States.
The Earth's crust is so waterlogged that fresh groundwater alone — not counting salty groundwater, which is even more abundant — outweighs all aboveground liquid freshwater 100 to 1. Much of it's too deep or blocked by rocks for us to economically reach, but we can still get to the roughly 1 million cubic miles closest to the surface.
In fact, some aquifers have been so heavily pumped that their water level has dropped too low for people to tap. Humans have overexploited many aquifers around the world, often trying to prop up an agriculture industry with a dwindling source of water.
Groundwater's quantity is far from the only concern, however; its quality is also under constant assault from a variety of sources. Natural poisoning of groundwater has long been known to occur around the world, as underground deposits of arsenic, heavy metals or even radon can seep into an aquifer and contaminate its contents. It's also possible that toxin-producing bacteria can naturally infiltrate an aquifer, despite the cleansing effects of soil and rocks above.
But humans indirectly pose an even greater threat to many aquifers — and to the fellow humans who drink from them. Although more Americans get their drinking water from surface sources like lakes and rivers, there are more water systems nationwide that use groundwater as their source than surface water (about 147,000 to 14,500), and hundreds of thousands more people who use private wells. And just as these wells are scattered throughout the country, often in remote rural areas, so are the diverse sources of pollutants that contaminate them.
What is runoff?
Runoff in general is a daunting enemy. Whenever it rains — or when a large amount of snow or ice melts — an inconspicuous yet widespread flood of water
For a planet where water covers 70 percent of the surface, Earth certainly makes its residents work hard for a drink. Aside from fish and other saltwater-sipping sea life, most of us have to share what little freshwater we can find on land.
And that's no small task. Only 3 percent of all water on Earth is freshwater, more than two-thirds of which is locked up in glaciers and ice caps. Of the other third, barely a trickle collects on the surface — lakes, rivers, streams and swamps represent less than 0.5 percent of all freshwater worldwide.
So where's the rest of it? An estimated 2.5 million cubic miles of freshwater are neither frozen, floating nor flowing on the surface, yet they account for at least 30 percent of total freshwater on the planet. Don't bother looking on the planet for all that water, though; it's actually in the planet. And while such a hidden location usually makes this underground ocean of freshwater safer to drink, it can also make it more dangerous — something the EPA recently acknowledged when it announced plans to crack down on the country's biggest water polluters.
What is groundwater?
Groundwater is simply water — mainly from rain and snow, but also from some human activities — that has soaked into the soil. That's the end of its journey from our perspective, but the water keeps going long after it's gone underground. It percolates downward, with dirt and rock particles filtering out dangerous bacteria as it sinks. When it finally reaches an impermeable layer of bedrock deep below the surface, it stops and begins to saturate the surrounding soil. Over many millennia, this pool of purified groundwater can grow into vast subterranean aquifers.
Some groundwater may eventually become encased in rock thanks to gradual geologic shifting, forming pressurized pockets known as "confined aquifers." These require complex drilling and pumping operations to extract their contents, leaving such deep deposits mainly for industrial uses such as large-scale farm irrigation. Other groundwater deposits are limited only by water supply and the bedrock below, and these "unconfined aquifers" make up the majority of residential groundwater sources in the United States.
The Earth's crust is so waterlogged that fresh groundwater alone — not counting salty groundwater, which is even more abundant — outweighs all aboveground liquid freshwater 100 to 1. Much of it's too deep or blocked by rocks for us to economically reach, but we can still get to the roughly 1 million cubic miles closest to the surface.
In fact, some aquifers have been so heavily pumped that their water level has dropped too low for people to tap. Humans have overexploited many aquifers around the world, often trying to prop up an agriculture industry with a dwindling source of water.
Groundwater's quantity is far from the only concern, however; its quality is also under constant assault from a variety of sources. Natural poisoning of groundwater has long been known to occur around the world, as underground deposits of arsenic, heavy metals or even radon can seep into an aquifer and contaminate its contents. It's also possible that toxin-producing bacteria can naturally infiltrate an aquifer, despite the cleansing effects of soil and rocks above.
But humans indirectly pose an even greater threat to many aquifers — and to the fellow humans who drink from them. Although more Americans get their drinking water from surface sources like lakes and rivers, there are more water systems nationwide that use groundwater as their source than surface water (about 147,000 to 14,500), and hundreds of thousands more people who use private wells. And just as these wells are scattered throughout the country, often in remote rural areas, so are the diverse sources of pollutants that contaminate them.
What is runoff?
Runoff in general is a daunting enemy. Whenever it rains — or when a large amount of snow or ice melts — an inconspicuous yet widespread flood of water
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