Why Regular Testing Is Crucial
The Difference Between Drilled and Dug Wells – What You Need to Know About Your Water Quality
For those who own a private well, water quality is crucial for both health and daily use. Changes in taste, odor, and color of the water are often the first signs that something is amiss. But the differences between drilled and dug wells are important to understand, as they affect which problems are most common and how water samples should be interpreted.
A drilled well draws its water from deeper groundwater reservoirs in the bedrock. The water often has a long residence time in the ground, providing natural filtration. A dug well, on the other hand, is usually shallower and draws its water from more superficial soil layers. It is more affected by precipitation, surface water, and activities in the surroundings. These fundamental differences explain why problems with taste, odor, color, and bacteria often differ significantly between well types.
When Taste Changes – Different Causes Depending on Well Type
In drilled wells, taste changes are commonly due to naturally occurring substances in the bedrock. Iron and manganese are two of the most common causes of metallic or bitter taste. In coastal areas, high salinity can also affect the taste, and in some regions, fluoride at high levels can give an abnormal taste. These substances do not always pose a health risk, but they often affect the usability of the water and may require some form of water treatment to make the water more useful in daily life.
Dug wells, instead, more often suffer from taste problems related to surface water impact. Organic material from leaves, plant debris, or humus can give an earthy or musty taste. Influence from nearby sewage or animal husbandry is also common, and the taste can change quickly after rain or snowmelt. For owners of dug wells, taste changes are often a signal that the well is inadequately protected against external influences and that measures may be needed.
Odor Problems That Reveal the Origin
A common odor in drilled wells is hydrogen sulfide, which gives a distinct rotten egg smell. This is often due to anaerobic conditions in the bedrock combined with the activity of sulfate-reducing bacteria. The odor is rarely dangerous in itself but can make the water practically unusable in daily life. Many well owners find that the odor worsens when the water has been stagnant for a while, for example in the morning or after a holiday.
In dug wells, odor problems are often linked to bacterial growth, ingress of surface water, or stagnant water in the well itself. A musty or earthy odor is common and should always be taken seriously. Unlike the hydrogen sulfide odor in drilled wells, which is often related to geology, odors in dug wells usually signal a hygienic problem that requires action. A water test can clarify what is causing the odor and if there are bacteria or other contaminants.
Color Changes Tell Different Stories
Brown, reddish, or black water in drilled wells is most often due to iron or manganese. Iron gives a reddish-brown color, while manganese can give a grey-black hue. The color can vary over time and often becomes clearer with higher water extraction, for example, when the whole family showers in the morning or when the garden is irrigated. Many well owners also notice that the water becomes more discolored during the summer when water consumption is higher.
Dug wells, instead, more often suffer from turbidity after rain, a yellow-brown color from humic substances, or visible particles from the bottom or well walls. These color changes are often a direct sign of inadequate protection against surface water. After heavy rains or snowmelt, the situation can worsen significantly, and some well owners see the water become turbid within hours after a heavy downpour. This is a clear indication that surface water is entering the well.
Bacteria – The Biggest Difference Between Well Types
When it comes to bacteria, the difference between drilled and dug wells is most pronounced. Drilled wells generally have a low incidence of bacteria thanks to the deep groundwater that has been filtered through the bedrock for a long time. When bacteria are nevertheless found, it is often due to faulty sealing around the casing, damage to the well cap or installations, or ingress from the surface. The presence of bacteria in drilled wells should always be seen as a warning sign and investigated thoroughly, as it indicates that something is wrong with the well's construction or protection.
Dug wells have a completely different risk profile. Here, bacteria are significantly more common and regularly occur in the form of coliform bacteria, E. coli, or enterococci. The causes are often surface water impact, nearby sewage systems, or animals in the surroundings. For owners of dug wells, it is not uncommon to find recurrent bacterial findings during sampling. In such situations, the well should be thoroughly inspected or supplemented with some form of treatment, such as UV light, to ensure safe drinking water.
Water Testing Provides Objective Clarity
Many problems in well water are visible, smell, or taste – but far from all. Some contaminants and bacteria can be present in the water without giving any obvious signs at all. Therefore, regular water tests are the only reliable method for obtaining an objective picture of water quality. Sampling is particularly important when there are changes in taste, odor, or color, after periods of heavy precipitation, when ownership changes, or after long periods of inactivity. As a general rule, chemical analyses are recommended at least every three years and bacterial tests annually.
For owners of dug wells, it may be wise to take bacterial samples more often, especially in the spring after snowmelt and in late summer when groundwater levels are lowest. Drilled wells rarely require such frequent checks, but at the slightest suspicion of a problem, the water should always be analyzed.
Summary
Drilled and dug wells differ significantly when it comes to common water quality problems. While drilled wells are more often affected by naturally occurring metals and chemical substances from the bedrock, dug wells are more exposed to bacteria and direct impacts from surface water and the environment. For you as a well owner, knowledge of your well type is an important prerequisite for correct sampling, accurate interpretation of analysis results, and appropriate measures when problems arise.
At svensktVattenprov.se, the focus is always on providing a reliable basis for safe and usable well water – regardless of well type. Through regular sampling and proper knowledge of your well, you can ensure that your household has access to clean and safe water, year after year.