How Does Well Water Work? Your Well System Explained

Reviewed by: James Layton
Updated on:
February 27, 2024

Key Takeaways

  • To understand how a well works, you must understand the role of each of these components.

How Does a Modern Well Work?

These days, water isn’t fetched with a bucket and pulley system, at least, not in the US. Rather than being dug by a shovel-wielding settler, wells are drilled with a portable drilling machine called a rig.

A drilled well consists of a hole bored (a borehole) into the ground, with the upper part or the entire depth of the well being lined with casing made of steel or PVC plastic.

The casing prevents the collapse of the borehole walls and prevents contaminants from entering the well water supply. The casing also provides a housing for a pumping mechanism and for the pipe that moves water from the pump to the home.

Borehole wells penetrate deep into the aquifer to ensure a reliable supply even in times of drought or high usage. This depth will vary depending on the depth of the aquifer, usually ranging from 100 to 800 feet deep.

Modern wells work with a series of components, the purpose of which is to move clean groundwater from the aquifer to the home.

To understand how it works, you need to know about the essential components of a well system, starting with aquifers.


After precipitation flows through various levels of soil and rocks, it collects as groundwater in pockets of water beneath the Earth’s surface called aquifers.

The top of an aquifer is called the water table. Aquifers replenish themselves thanks to nature’s water cycle, but there are instances where excessive pumping of the water lowers the water table or dries out the aquifer entirely.

While not necessarily part of the well system itself, an aquifer is absolutely essential to a well system because it provides the water, without which there wouldn’t be much point to the other well components.

Well casing

After a well is drilled into the aquifer, it is lined with the well casing. The well casing will be at least 25 feet long, usually longer. It prevents collapse of the borehole and keeps out surface contaminants.

Made of either steel or plastic, well casings can occasionally bend or crack. Fixing a cracked well casing can cost anywhere from a few hundred to a few thousand dollars, but it’s crucial to maintain your well casing. A cracked well casing can allow contaminated surface water into your well.

The layers of earth between the surface and the water table act as natural filters, so that by the time water makes its way to the aquifer, many surface water pollutants have been removed or reduced.

However, contaminated groundwater is not uncommon, especially for homes built near industry and agriculture. It’s essential to have your well water tested annually to make sure your groundwater is safe to drink. Depending on the results, you’ll probably need some kind of filtration system for your well water.

See our reviews of the best whole-house water filters for well water for more information.

Well screen

You may wonder how the water gets in if the well casing is made of steel or plastic. Below the water table, the well casing becomes a well screen. This screen allows in water from the aquifer but keeps out sediment.

Well screens are usually made of steel but can also be made of plastic or fiberglass.

In extreme cases, bacterial growth, acidic water, or high chlorides can cause corrosion of the well screen, which can lead to “sand pumping” and degrade the well pump components.

If this happens, you’ll have to repair the screen and potentially repair or replace the well pump.

Well pump

The well pump is powered by electricity to pull water from the aquifer. There are two types of well pumps.

Jet pumps are above ground pumps used for shallow wells less than 25 feet deep, and submersible pumps are used for deeper wells. Submersible pumps are installed within the well casing and pull water from the bottom of the well.

A submersible well pump is much more common than a jet pump and connects to the pressure tank in the house through the pitless adapter and underground pipelines. Approximately 60% of US residential wells are submersible pumps, as opposed to 32% that use jet pumps.[1]

Have a look at the best submersible well pumps and the best shallow well pumps for more information about well pumps in general.

Pitless adapter

A pitless adapter connects the well pump to the service pipe that leads into the home. It’s installed below the frost line to ensure the service pipe doesn’t freeze.

They’re called “pitless” because before pitless adapters, well pits were common for the same purpose, but they caused all sorts of problems, like flooding and children falling into them. They’ve been outlawed in most states.

Well cap

The well cap is the visible part of the well that you can see. You can access the well through the cap to conduct repairs and maintenance of the well and its machinery.

Well caps protect your well water from pollutants in surface water. To ensure the well cap is able to fulfill this role effectively, it should be about 18 inches above the ground and always sealed watertight.

When a well cap is damaged or otherwise not sealing out surface water, bacteria and other impurities can contaminate your well water, just as with a damaged well casing.

Pressure tank

The pressure tank stores the water pumped from underground so you can use it throughout the day. They can hold anywhere from 20 to 80 gallons of water.

The pressure tank stores water under pressure, delivering water to fixtures throughout your home even after the well pump has turned off. It’s fitted with a pressure sensor that activates the pump whenever the water pressure gets lower in the pressure tank. 

You may need to make use of a booster pump if water pressure throughout the home is not as high as you would prefer.

Check out our reviews of the best water pressure booster pumps.

Maintenance of a Private Water Well

1. Keep the well cap safe

Make sure the well has a tight seal and rainwater flows away from the opening. Keeping it well above ground level prevents flooding of the well cap. Otherwise, surface water may seep into the well’s opening and pollute the groundwater.

2. Water testing

According to the Centers for Disease Control and Prevention, you should have your well water tested annually for pH level, microbes, nitrates, lead, and more.

If you sense a difference in the smell, taste, or color of your tap water, you should have it tested right away. Construction in local areas and natural disasters can affect the quality of groundwater.

The most accurate way to test well water is to send a sample to an accredited laboratory, such as Tap Score.

3. Hire professionals

When it comes to repairing or replacing a well or any of its components, you can DIY some of it.

For example, you can easily maintain a pressure tank yourself and even DIY a water pressure tank installation if you’re a rather handy person.

However, for most well system problems, you’ll want to hire a professional.

Cost of a New Well

Sometimes a well must be drilled either because the original well dried up or it’s a new property. I go into detail about how a well is drilled in another article, but here’s a general idea of the costs.

A new water well will cost you around $5,500 for a depth of up to 150 feet, with the general price range falling between $1,400 to $12,000 for wells of varying depths.

How City Water Differs From Well Water Systems

 City waterWell water
TasteFaintly chlorinatedBitter if it has iron or sulfur
MaintenanceOnly of personal filtration equipmentConsistent: annual testing, water treatment, well servicing, etc.
CostPayment to water company and for personal filtration devicesNo water bill but maintaining the well and treating the water are your responsibility
HealthTest and treat for contaminantsTest and treat for contaminants

Final Thoughts

If you’ve recently purchased a home with a well, don’t worry. You won’t be pulling a bucket up out of the ground. But knowing the inner workings of how a water well works will make you more aware of the well’s maintenance needs.

It’s a complex process, but knowing the different components of a well can help you understand how it works.

We at Drinking Water want to help you maximize the benefits of owning a private well. Check out some of our other articles to get the most out of your well system:


1. Environmental equipment and supply. Water well pumps.

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