Well water drilling: All your questions answered
Private wells are one of the most complicated utilities that homeowners are tasked with running. From drilling to filtering, there’s a bunch of obscure knowledge to get your head around.
To help you become a well water expert, here are answers to some of the most commonly asked questions about how wells are located, drilled, and function.
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What is a water table?
The water table is a term for describing the depth where the earth becomes full of water.
At a certain level underground, the spaces between hard matter are saturated with water, known as groundwater. The upper limit of this zone is the water table.
Where is the water table located?
How far down the water table and groundwater is located depends upon features of the surrounding environment. Areas with traditionally high rainfall and porous rock are likely to have higher water tables.
Some water tables may exist just under the surface, while others can be tens of thousands of feet down.
The easiest way to find out where the water table is to measure the depth of nearby existing wells.
Drilling companies may also use electric or acoustic probes to gain an indication. However, judging the location of a water table is often not an exact science.
What is the average well depth?
Because the depth of the water table can vary, there is no average well depth. However, most household private wells are drilled to a depth of between 150 to 850 feet.
Because well depth has a large effect on the cost of drilling, many people want to get an idea of how deep their well will be before they commit to the project.
While there’s no surefire way of knowing where the water table lies on your property, looking at the depth of neighbors’ wells should give you some indication.
How deep should my well be?
Most wells should extend down below the water table in order to create pressure that helps the water to naturally rise up the well shaft.
Exactly how far a well needs to drop below the table depends upon rock composition. Some wells may need to drill down hundreds of feet to achieve the same pressure (measured in gallons per minute) as those close to the surface.
Investing in a sufficiently deep well is worthwhile, as it can be difficult to artificially increase water pressure.
Once water passes through a filtration system and is connected to multiple appliances and faucets, water pressure can suffer.
How much does drilling a water well cost?
Most estimates place the cost of a new well at between $2,000 and $12,000, depending on the depth and type of drilling needed. Various factors like labor, trenching, and well filtration costs are at play. The best whole house water filters for well water can sometimes cost as much as $8,000.
Most drilling companies charge per foot, with the price rising if the terrain is complex or the rock is especially hard. Hard rock requires the use of more technical drill bits that may need to be replaced several times.
While the costs of install and running a well are significant, remember that they’re offset against savings on municipal water bills.
How do you know when you’ve hit water when drilling a well?
When a borehole reaches layers of looser, sandier earth or gravel, the drill meets less resistance, and the water table is often near.
At this point, well drillers will often slow down and take repeated samples as they go.
The less porous the rock, the deeper wells will likely have to be drilled. For example, wells in limestone or slate will likely be much shallower as they are more permeable.
How Does a Water Well Drilling Rig Work?
There are two main types of drilling rigs for water wells. Rotary drillers drill into the ground in a circular motion, while cable tool drills use a ‘fence posting’ technique, pounding a heavy weight into the earth.
Both types of rigs use different drill bits depending on the terrain and monitor important factors like temperature and pressure.
What is an artesian well?
Artesian wells tap into naturally pressurized groundwater sources, which means that the water is able to rise to the surface without the use of a well pump.
In this sense, artesian wells can be thought of as a mid-point between wells and natural springs.
Artesian well diagram (Source: Science Direct)
How do artesian wells work?
The aquifers storing the water for artesian wells are usually found at a lower depth than the surrounding water table, underneath a layer of impermeable rock.
It’s this inability to reach the water table that creates hydrostatic pressure pushing the water upwards.
Are artesian wells the best kind of well?
Water companies sometimes use the ‘artesian’ label to conjure images of pristine spring water. While it’s true that some artesian wells offer a higher level of natural filtration, resulting in purer water, the same can also be true of regular wells.
Does artesian well water need filtering?
All well water, whether from an artesian well or not, should be tested for contaminants on a regular basis.
Artesian wells may be less contaminated than regular wells on average, but there’s no guarantee that any individual artesian well or spring is free of unwanted substances.
After you get the results of your well water test, you can decide whether you only need a simple sediment filter to remove small particles, or a more extensive well water filter system.
What is water dowsing (water witching)?
In some parts of the world, there’s a small industry of water mystics who claim to be able to use folk methods to identify or “divine” the best place to drill a well on a property.
The most famous of these methods is called water dowsing or diving. Dowsing involves using two rods or a single forked stick to survey the earth and sense the location of accessible groundwater. A person who practices dowsing is often referred to as a water witch.
A man practicing water dowsing in the UK in the 1940s (Source: USGS)
How does water dowsing work?
Dowsing rods are usually made from canes, twigs, or metal rods. The diviner will pass these rods over an area of ground, observing for any indications that the rod is responding.
Many believe that dowsing rods will converge on the spot where water or other hidden objects are closest to the surface.
Whether or not water dowsing actually works is a source of much debate in many communities. We do know that, when subjected to scientific analysis, the case for dowsing universally falls apart. Here are two videos by famous skeptics debunking the credibility of dowsing—one from Richard Dawkins, the other by James Randi.
However, dowsing has a long history, filled with anecdotal examples of success. This suggests that many who practice it do have some ability to judge groundwater features, even if it’s not through some special property of the dowsing rods themselves.
Do people still use dowsing?
Some communities possess a go-to water well person—often an elder or designated water witch—who is known for their ability to find the best drilling locations. Many of these people explain their skills through their use of dowsing.
Every few years, reports emerge of large companies also employing the services of water diviners to help them drill wells or uncover the location of old, forgotten pipes. For example, NPR covered water companies from the UK that regularly use dowsing in this article from 2017.
