How do Water Wells Work?

 For many people in the world, they get their water supplied to them through pipes in their house or apartment. However, for the rest of the world not hooked up to centralized water, they get their water through either private or public wells. ‘

Wells are some of the most essential components to developing a sustainable society. They provide a clean and reliable supply of water for drinking, bathing, and irrigation, even in locations where water on the surface is scarce.

Wells are essentially just holes in the ground filled with water, but they have more complexities than meets the eye. Let’s take a closer look at how wells work.

How wells work

Wells historically have been dug by hand. They essentially are just holes in the ground whose depth goes below the water table. The water table is the level of groundwater below the surface.  Nearly everywhere on earth has a water table below the surface, but in some places it’s a few feet and in others its a few hundred feet.

The water table isn’t just an underground open lake though, it’s dirt and rock just like everywhere else, except the groundwater fills in the spaces between the particles. In days of old, workers would just dig a hole until the hole started filling up with water.

As long as the hole depth stayed below the water table depth, the hole would continuously fill up with water.

Many wells in remote places are still dug by hand, but most are now dug by drilling machines that can create much more uniform and far deeper wells.

All that said, there are a few different types of wells that are important to talk about & define.

Dug wells

Dug wells are ones made by hand with simply a shovel. They’ll only be possible in places with a high water table and soft ground. Once a digger reaches the water table, the hole is typically lined with stone to stabilize it. These wells typically can’t be much deeper than the water table, as you can’t dig past the water table with a shovel, the hole will just keep filling in. This is the same phenomenon you’ve likely experienced digging a hole in sand at the beach.

Driven wells

Driven wells are made from small-diameter pipes which are driven into soft ground. These pipes typically have screens at their bottom to filter out sand and particulate matter and can be an effective, quick and simple way to make a well. However, they have some drawbacks. They can really only reach shallow water and contamination from the surface can occur easily.

Drilled Wells

Drilled wells are likely the most common type of wells today, but they also are the most complicated and expensive to make. They are drilled using massive drilling rigs which can go through all types of earth. These wells are typically very deep, upwards of 1,000 feet, and are used to reach very deep water reserves.

Now that we’ve gone through different types of wells, let’s learn a little bit more about how they actually function

Wells fill up based on the groundwater level, like we mentioned. Once you take water from the well, water from the surrounding groundwater slowly starts filling the well up again. The rate of this refilling has to do with how much groundwater surrounds the well and the size of the particles in the ground. If the particle space is large, the water will fill faster. If the well is in fine clay, the well will take a while to refill.

For most wells, a pump is placed into the wells to suck out the water. When water is pumped out and the surrounding water tries to refill the well, something called the cone of depression forms.

This cone of depression is essentially a conical depression in the water table which can extend far beyond the well. In fact, if a high flow rate well is installed too close to another well, the first well’s cone of depression can draw the surrounding water table down so far that the neighboring wells no longer work.

There are formulas engineers use to calculate and model cones of depression when designing wells, which is crucial to make sure your well doesn’t adversely affect anything else.

It’s also crucial to make sure that your well doesn’t overpump the water table. If you suck too much water from the ground, eventually the ground can compact and the water table will drop permanently. This settling can cause the elevation at the surface to go down, in some cases many hundreds of feet over years of well pumping. This has occurred in regions of the US like in California and towards the west coast.

While there are a plethora of public wells that supply water for entire cities, let’s focus in on private wells to understand a little bit more about what goes into them. Many people across the world supply their own water through private wells. These wells will be drilled near their dwelling and will have a screen at the bottom to filer out grit, a submersible pump placed at the bottom of the well along with electrical wiring to power the pump. Then there will typically be tank above ground that pressurizes the water, giving your house pressurized water to use in sinks, faucets, toilets, and showers.

It’s really as simple as that. The main components of wells are:

Well casing: which is the solid tube structure of the well

Well cap: which is the cover of the well placed at the surface to keep animals or other debris from falling in and contaminating the well.

Well screens: which are placed at the bottom of the well to keep sediment out and keep the well from filling up with dirt.

require a number of technical factors to be considered when creating and designing them. This article focused primarily on the basics of wells, but there’s some more technical concepts we skipped over. Things like aquifers, water head, calculating flow rates & water volume, and other uses for wells besides purely water collection, to name a few. Hopefully though, this was enough to give you a good introduction to the science of water wells.



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