How Deep Should a Water Well Be? Depth Guide by Region
The depth of your water well depends entirely on your local geology and water table — you don't get to pick a number. Most residential wells in the United States are 100 to 400 feet deep, but some areas require wells over 500 feet. Understanding what determines depth helps you budget accurately and set the right expectations.
Typical Well Depth by Region
| Region | Typical Depth | Common Geology |
|---|---|---|
| Southeast (FL, GA, SC) | 50 – 200 ft | Sand, limestone, clay |
| Northeast (PA, NY, CT, MA) | 100 – 300 ft | Granite, shale, glacial deposits |
| Midwest (OH, MI, IN, IL) | 50 – 200 ft | Glacial till, limestone, sandstone |
| West (CO, AZ, NM, CA) | 200 – 500 ft | Hard rock, deep aquifers, arid conditions |
| Pacific Northwest (OR, WA) | 100 – 300 ft | Basalt, volcanic rock, alluvial deposits |
Your well driller will have experience with local conditions and can usually estimate depth before drilling begins.
Understanding the Water Table
The water table is the underground level below which the ground is saturated with water. Think of it as the top surface of an underground lake that follows the terrain.
Key facts about the water table:
- It rises after heavy rain and drops during droughts
- It's deeper in hilly areas and shallower in valleys
- It can change over time as groundwater is pumped
- Your well needs to be drilled well below the water table to ensure year-round water
A well driller typically drills 20–50 feet below the static water level to ensure adequate supply during dry seasons.
Shallow Wells vs. Deep Wells
| Feature | Shallow Well (<50 ft) | Deep Well (>50 ft) |
|---|---|---|
| Cost | $3,000 – $7,000 | $6,000 – $30,000 |
| Water quality | More vulnerable to contamination | Generally cleaner, more filtered |
| Water supply | May run dry in drought | More reliable year-round |
| Pump type | Jet pump or hand pump | Submersible pump |
| Contamination risk | Higher (surface runoff, septic) | Lower (natural filtration) |
| Maintenance | Easier pump access | More expensive pump pulls |
How Geologists Determine Well Depth
Before drilling, professionals use several methods to estimate depth:
- Well logs from nearby properties — the best predictor of your well depth is what neighbors found
- Geological survey maps — USGS maps show aquifer depths and formations
- Hydrogeological studies — for commercial or high-yield wells
- Test drilling — in uncertain areas, a small test bore can determine conditions
- Local driller experience — experienced drillers know their area well and can give accurate estimates
How Depth Affects Cost and Water Quality
Cost: Every additional foot of depth adds $25–$65 to your total. A 400-foot well can cost twice as much as a 200-foot well. Deeper wells also require more powerful (and expensive) submersible pumps.
Water quality: Deeper wells generally produce cleaner water because the water has been naturally filtered through more rock and soil. However, deep wells are more likely to have elevated levels of naturally occurring minerals like iron, manganese, arsenic, and hydrogen sulfide.
Frequently Asked Questions
Can I choose how deep my well is drilled?
No — the driller must go deep enough to reach a reliable water-producing zone. You can't stop at 100 feet if the water is at 200 feet. However, once adequate water is found, you can discuss with your driller whether to go deeper for additional supply.
What happens if the driller doesn't find water?
This is called a "dry hole." Most drillers will attempt a second location on your property. You'll typically still owe for the footage drilled on the dry hole ($25–$65/ft). Some drillers offer dry-hole guarantees — ask about this before drilling.
Is deeper water always better quality?
Not necessarily. Deeper water is generally more filtered and less vulnerable to surface contamination, but it can contain higher levels of dissolved minerals, iron, sulfur, and arsenic. Always test your water regardless of depth.
How do I find out how deep my existing well is?
Check your well completion report (well log) — this was filed with your state when the well was drilled. You can also contact your county health department or water management district. If no records exist, a well service company can measure the depth.