Key Takeaways
- Well water comes from groundwater hidden either deep underground or just below the surface.
- Groundwater is stored in aquifers, of which there are two kinds: confined and unconfined. This will determine what kind of well you need, and how deep it should be.
- The deeper the well, the less likely you are to encounter contaminants from surface runoff.
- To ensure the quality and safety of your drinking water, consider using Tap Score’s water testing kits.
Where Does Well Water Come From?
Well water originates from vast subterranean reservoirs of groundwater known as aquifers, porous rock layers that can exist near the Earth’s surface or extend as deep as 30,000 feet.
Contrary to popular belief, groundwater is not some River Styx flowing deep within the Earth.
Rather, an aquifer is made of small rocks, gravel, and unconsolidated sediment that holds water in the tiny spaces between the particles.
Think of it like a sponge that holds water in the tiny spaces between the foam. The aquifer works the same way, holding water in porous spaces in underground rocks. Water flows through these cracks and crevices.
To access this water, wells are drilled into these formations, typically ranging from 25 to 800 feet deep.
The deeper the well, the purer the water is likely to be.
A shallow well is more likely to need treatment because it’s closer to the surface, where contaminants from runoff are more abundant.
Here’s a list of the best whole-house well filters of 2024.
Saturated ground vs. unsaturated ground
Groundwater is actually present in two zones: unsaturated and saturated.
The unsaturated ground is present just below the land surface. It holds water and air in tiny open spaces between the ground particles. These particles could be sand, sediment, gravel, or tiny rocks. Water isn’t a major part of the unsaturated zone.
As the ground gets deeper, it becomes more permeable, and small fractures and spaces between rocks hold a large amount of water. This is known as the saturated zone, or an aquifer, which is the main source of groundwater.
Water table
The water table is nothing but the line that separates an unsaturated zone from a saturated zone. When the well is dug, the moment it hits the point where water starts coming out of the ground is called the water table.
Where does the water come from?
If you remember the water cycle from elementary school, then you already know the answer. Water from lakes, rivers, and oceans evaporates, transforms into clouds, and then rains down in a perpetual cycle.
Surface water that doesn’t end up in bodies of water gets absorbed by the ground.
Water flows through the porous sand and gravel, where soil also acts as a natural filter and removes some of the impurities present in the water. The process continues until water meets the underlying aquifer.
Types of Aquifers
Unconfined aquifers
An unconfined aquifer is the common groundwater source that shallow water wells like “dug wells” and “borewells” use to draw water from.
They are often called “the water table,” which is also their upper boundary. They are not confined by any underground layer and are easiest to access. However, they’re more prone to contamination because of surface pollutants.
Unconfined aquifers are formed at higher rates and are affected by rainfall. In droughts, unconfined aquifers are at risk of drying up, and the water table may fall farther below the surface.
Confined aquifers
As is obvious from the name, these aquifers are confined by a layer of impermeable bedrock and clay. In other words, water stored in the confined aquifer can’t move past such a layer.
Since the confined aquifers are bound by bedrock, the water present here doesn’t come directly from above the ground like in the case of an unconfined aquifer, which is replenished by rainwater.
Instead, the water comes from sources present at higher ground. For a much better explanation, see this YouTube video from the University of Minnesota Extension.
Sometimes, this confinement between two confining layers raises the pressure in the aquifer. If you drill a well into such an aquifer, water will gush out of the hole due to pressure differences.
Such wells are also called artesian wells. There is no need for a water pump.
Modern drilled wells that tap into confined aquifers offer a more consistent supply of pure water.
How Do Wells Get Water From Underground?
At its simplest, a well is a hole in the ground that is deep enough to tap into an underground aquifer and draws water by some kind of mechanical system.
In earlier days, it was a pulley-and-rope system, but now modern water wells use submersible pumps.
If you’re in the market for a submersible pump, be sure to consult our list of the best submersible pumps before you buy one.
Now, wells go much deeper, thanks to high-tech rotary drilling machines and jet pumps! So, you don’t have to worry about fetching water like some cowboy in an old western movie.
You can find more about how private wells are drilled here.
Do Wells Run Out of Water?
Yes, wells do run out of water.
This usually happens in shallow, unconfined wells where drought and other factors are present. Basically, it happens when the water table falls below the level of the well.
In such cases, the depth of the well needs to be increased. It’s not likely, but it can happen.
If your well taps into a confined aquifer, it’s less likely to run dry.
How fast does well water replenish?
Groundwater is sometimes hundreds or even thousands of years old. According to one estimation, the recharge rate of groundwater is between 0.3 and 15 inches per year.
The replenishment of well water is a continuous process. There is no right answer for this because the rate at which well water replenishes varies from location to location.
How to Find Groundwater Under Earth’s Surface
Where to dig for groundwater is the most common query by homeowners in need of a well. There are many false beliefs and opinions regarding this, mostly based on superstitions and personal anecdotes.
Allow me to challenge those misconceptions.
Hydrogeology
Hydrogeology is the study of Earth layers and groundwater. With the use of modern technology and drilling machines, hydrogeologists can locate suitable aquifers for drinking water and irrigation. They also examine soil samples from nearby wells and look for contaminants.
All local well contractors have expert hydrogeologists on their teams to pinpoint the highest-yielding locations.
Water dowsing
Charging money for finding water using metallic rods and sticks is quite common in rural locations, and it’s called water dowsing. They claim to have some sort of reaction to energy fields generated by groundwater.
However, it’s all hocus-pocus and has nothing to do with actual science.
But you might wonder why these guys succeed in finding an aquifer?
It’s because underground aquifers are present everywhere. So, the chances of striking the water table are quite high.
Groundwater Contamination: Is it Serious?
Well water is safe to drink, but annual testing of your well water is crucial.
In many cases, water treatment and filtration designed especially for well water are required to avoid possible health hazards associated with contaminated groundwater.
Find the best water filtration system for well water on this list of our favorites.
Typically, kids, the elderly, and the chronically ill are the most sensitive to contaminants in well water, but, really, contaminated water can affect anyone.
To test your well water, you can use DIY testing strips, but they don’t test for all impurities, for example, fluoride. For a complete and accurate analysis, it’s best to go through a water testing laboratory.
Here are some of the most common contaminants that affect groundwater and, by extension, well water:
Pesticides and fertilizers
These may be necessary for effective crop harvesting (debatable), but the toxic chemicals from pesticides move through the soil and end up in an aquifer, and fertilizers can pollute groundwater with nitrates (and the alleged negative outcomes of conventional agriculture don’t stop there).
Mining waste
Mining waste, while rare, produces a chain reaction of contamination that can make its way to residential wells. According to the US Geological Survey, industrial waste from mines can expose users to sulfuric acid, dissolved iron, copper, lead, mercury, and bacteria.
Other industrial operations have irresponsibly disposed of waste and contaminated groundwater with not only those listed above, but also chromium, benzene, and myriad other chemicals and heavy metals.
Road salt
Road salt prevents ice formation on roads in winters, but it also corrodes pipes and can lead to leaching of heavy metals, including lead. It can also increase sodium consumption in humans.
According to the New Hampshire Department of Environmental Services, deicing efforts use 50% to 75% more salt than is necessary. The state of Wisconsin has even begun to use cheese brine for deicing rather than sodium chloride.
Human and animal waste
E. coli bacteria is most commonly found in fecal matter and can sneak its way into well water, along with other contaminants from wastewater.
How, you ask?
Well, if you’re on well water, the odds are you also have a septic tank. After your septic tank separates the liquids and solids, some of that wastewater filters back into the groundwater. And if your septic tank is cracked or leaking, all bets are off. Anything from your septic tank can leak out of it.
The soil cleans much of it naturally, separating the water from the contaminants as it percolates further and further beneath the surface, but not all. And if your well is shallow or damaged, it makes the chances even higher that waste matter can contaminate your drinking water.
In addition to your septic tank, fecal matter can also come from wild animals or nearby farms.
It might take a lot of wild animals to contaminate your groundwater, but it’s not impossible. And if there’s a dairy farm down the road, the chances are even greater.
It’s important you follow recommended guidelines for servicing and repairing your well, keeping your septic tank the required distance from your well, and having your water tested annually to ensure your well water is not contaminated by your wastewater.
See this information from the EPA for more information about well water and sewage risk.
The best way to clean bacteria and other pathogens from well water is to use an ultra-violet light purifier. Read up on the best UV purifiers of 2024 for more information.
Nitrates
Nitrate is a potentially dangerous but all too common contaminant. It’s naturally occurring but can also be caused by fertilizers, animal agriculture, and even your septic tank.
Consuming nitrates over the EPA’s safe level can result in birth defects, certain cancers, thyroid disease, and more.
Arsenic
Arsenic is a naturally occurring element in rock and is sometimes found in deep private wells.
Unfortunately, it is harmful to humans and can even lead to cancer. Studies show that industrial waste containing arsenic is the leading cause of such contamination in groundwater.
If you’ve had your water tested and discovered it’s contaminated with arsenic, read our review of the best whole-house filters that can remove arsenic from your drinking water.
Lead
Lead isn’t present in groundwater but gets dissolved by corroded lead pipes and lead-containing plumbing fixtures, making its way into your groundwater not through your well, but your home’s plumbing system.
This is concerning because the dangers of lead are well established, and, in fact, the EPA has placed the safe limit for lead in water at a whopping ZERO.
We’ve conducted a review of the best water filters for lead removal to help you keep your family safe.
Final Thoughts
Groundwater is the most consumed natural resource on the planet, so much so that the survival of humankind depends on it.
Hopefully, knowing about its origin and how it works beneath the Earth’s surface will help you consume water more responsibly. It’ll also help you keep your private well healthy and running.
Like any other natural source, it has limits, and regulating its usage will ensure a lifetime of fresh water supply without any interruption.
Read our comprehensive well water treatment guide to become the most informed well water user in your neighborhood.
We at Drinking Water are committed to presenting readers with well-researched and thoroughly curated articles to help you understand drinking water and how to maintain it.
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