Love and wells have something in common — the deeper they are, the better. If you’re shopping for your dream home but are concerned about residential water quality, well depth foreshadows what you can expect.
Before signing on the dotted line, it pays to know how deep a well for drinking water should be — 100 feet or more is a good target.
Stick around to learn why.
- For drinking water, a well should be dug to a depth of at least 100′ feet below the ground surface or 10′ feet below the water table.
- Deeper wells can range from 300′ – 600′ feet or more depending on the soil type and local regulations.
- To determine the optimum depth for your well, consult an experienced well driller or hydrogeologist.
- Deeper wells are more expensive to build, but they provide access to clean water that is less likely to be contaminated by surface pollutants or agricultural pesticides.
Where Does Well Water Come From?
Nearly all private well water comes from the ground. As rain and snowmelt seep into the soil, it fills the spaces between rocks. Known as the saturation zone, or water table, it’s the primary source of water for most shallow wells. Deeper wells tap the plentiful underground aquifers beneath the water table.
A properly constructed well should be drilled deep enough to guarantee a steady water supply and limit contamination.
How Does a Well Work?
A well is a hole in the ground dug deep enough to strike water. Lined with a well casing to prevent collapse, it’s equipped with an automatic well pump that draws water from the depths. To learn more about the inner-workings of well, read our post on how a well works.
How Deep Is an Average Well?
The average well depth is 100-500 feet, but depending on several factors from climate to geology, the depth ranges from as little as 20 feet to 1000 feet or more.
Factors Affecting Well Depth and Water Quality
Well drilling contractors consider these factors and more when estimating how deep private wells should be.
The Water Table
Ground water levels fluctuate with changes in the weather. Expect a seasonal rise in the spring as snowmelt from higher elevations reaches the surface. By late summer, shallow wells may run dry without enough rain.
Cyclical climate patterns also impact ground water levels. In areas where the climate is extreme, years of heavy rains followed by intermittent droughts complicate well drilling.
Wells should be deep enough to match the lowest possible water level, but calculating the depth needed can be a guessing game. Well contractors look closely at historical data before digging.
Your local geology can help or hamper your ground water quality.
Soil is a natural filter. So, in general, the deeper surface water seeps into the ground, the cleaner it will be. Most contaminants will have been removed by the time it reaches a depth of 100 feet. The deepest wells offer maximum ground filtration.
But not all soil types are created equal. Some soils retain more moisture while others repel water. And wells must be drilled deeper in areas where the bedrock is less permeable.
Well contractors consider the type of soil you have and the potential for contamination before making depth recommendations.
Your local county health department doesn’t monitor private water quality — well water testing is up to you — but they develop building codes to protect your area’s drinking water supply.
Using water table data, they set minimum well depth and pump placement guidelines. Before drilling begins, contractors have a ballpark estimate of how many feet deep your well has to be, and that helps determine what type of well you need.
Types of Wells
There are few different types of residential well systems with the common one being a driven well:
Drilled wells are the deepest. Fully encased and equipped with powerful submersible pumps, they can draw water from 1000 feet or more.
A driven well is a one-piece pipe punched into the water table. Deeper than a dug well but shallower than a drilled well, the average depth is just 50 feet. Because they draw water from closer to the surface, they’re easier to contaminate.
Dug wells are excavated with a backhoe and lined with concrete or tile to prevent collapse. The depth of the well depends on how far you have to dig to hit potable water.
Powered by an above-ground jet pump, most shallow wells are dug wells with an average depth of 30 feet deep. Some, however, lack a full well casing.
How Much Does a Drilling a Well Cost?
Well drilling is an imperfect art. Companies charge by the linear foot, and the deeper the well, the more it costs. A dug well could run as little as $2000 — drilling deep can set you back $15000 or more plus the price of the casing and pump.
Do Deeper Wells Mean Better Water?
While there are exceptions to every rule, deeper wells generally offer better water quality and are less likely to run dry.
A shallow well can produce as much clean water as a deep well depending on the circumstances, but they’re more vulnerable to flooding and drought. And the closer a well is to the surface, the more susceptible it is to contaminants.
But like any home improvement, homeowners should consider the return on investment. If the ground water in your area is clean and drilling deeper offers little benefit, save your cash.
If the alternative is no water or lower quality water that could contain harmful microorganisms and other contaminants, why risk it?
Budget is an important consideration, but when you can, it pays to invest in a top-quality private water supply that’s less likely to run dry. A good well safeguards your family’s health and improves the resale value of your home.
Should I Filter My Well Water?
Despite your best efforts, some wells won’t produce the premium water you hoped for no matter how deep they are.
Further reading: Do you need to filter well water?
But the good news is — you don’t have to resort to plastic bottles for clean tap water when a home well filtration system can remove impurities. Which type do you need? It depends.
Shallow wells are prone to chemical and bacterial contamination. An undersink reverse osmosis filter removes both from your drinking and cooking water, or you can choose a whole-house system that improves poor water quality home-wide.
Drilled wells rarely harbor bacteria, but large aquifers contain hard minerals. A water softener or salt-free conditioner removes excess calcium and magnesium and protects your home from limescale.
Whether you’re buying an existing home or new construction, well testing is required. The results will point you to the right filtration system.
Private wells have advantages. There’s no quarterly bill to worry about and you have more control over your water quality. But like love, depth matters.