Deep Wells Over 400 Feet: What to Expect
Many areas of San Diego County require wells deeper than 400 feet to reach reliable water. Deep wells present unique challenges—from higher drilling costs to specialized pump equipment to greater maintenance complexity. This guide covers what to expect when dealing with very deep water wells.
📋 In This Guide
Why Wells Go Deep in San Diego County
Areas Requiring Deep Wells
- Valley Center — Many wells 300-600 feet
- Ramona — Variable, some areas 400+ feet
- Julian/Mountain areas — Often 400-800+ feet through granite
- Fallbrook/Bonsall — Some areas 400-600 feet
- Borrego Springs — Deep aquifer access, 400-800 feet common
- Alpine/Jamul — Fractured granite, often 400-700 feet
Geological Reasons for Depth
- Granite bedrock — Water only in fractures, may be deep
- Falling water tables — Drought and pumping lower water levels
- Sedimentary layers — Deep aquifers beneath clay or shale
- Competition — Nearby wells draw down shared aquifers
Deep Well Costs
Drilling Costs by Depth
| Depth | Drilling Cost | Total Project* |
|---|---|---|
| 400 feet | $20,000-$40,000 | $30,000-$55,000 |
| 500 feet | $25,000-$50,000 | $40,000-$70,000 |
| 600 feet | $30,000-$60,000 | $50,000-$85,000 |
| 800+ feet | $40,000-$80,000+ | $65,000-$120,000+ |
*Total includes casing, pump, electrical, pressure tank, permits
Why Deep Wells Cost More
- Drilling time — More hours = more labor and equipment cost
- Drill bit wear — Hard rock wears bits, adds replacement costs
- Casing — More steel casing material needed
- Pump — High-head pumps for deep settings cost more
- Electrical — Longer wire runs, may need three-phase
- Installation difficulty — Handling equipment at depth is harder
Equipment for Deep Wells
Pump Selection
Standard submersible pumps are rated to about 300-400 feet. Deeper wells require:
- High-head pumps — Designed for 400-1,000+ foot settings
- More stages — Additional impellers to push water up
- Higher horsepower — More power to overcome lift
- Quality motors — Franklin, Grundfos, etc. for reliability
Pump Ratings
| Well Depth | Pump Head Rating Needed* | Typical HP |
|---|---|---|
| 400 feet | 500-600 feet | 1.5-3 HP |
| 500 feet | 600-700 feet | 2-5 HP |
| 600 feet | 750-850 feet | 3-7.5 HP |
| 800 feet | 950-1100 feet | 5-10 HP |
*Account for drawdown and pressure system requirements
Electrical Considerations
- Single-phase (230V) — Available to about 5-7.5 HP
- Three-phase (208/230/460V) — More efficient for 5+ HP motors
- Wire sizing — Longer runs require heavier gauge wire
- Voltage drop — Critical issue at 400+ feet; must be calculated
- Soft start/VFD — Recommended for large motors
Three-Phase Advantages
- More efficient (lower operating cost)
- Longer motor life
- Less heat generation
- Better starting characteristics
- Available in higher horsepowers
Water Quality in Deep Wells
Advantages
- Better protected — Less surface contamination risk
- More consistent — Less affected by seasonal changes
- Naturally filtered — Rock filtration removes particles
- Usually bacteria-free — Age and depth protect from pathogens
Potential Issues
- Harder water — More time in contact with minerals
- Higher TDS — More dissolved minerals overall
- Natural arsenic — Some deep aquifers have elevated arsenic
- Hydrogen sulfide — "Rotten egg" smell in some formations
- Thermal water — Very deep water can be warmer
Testing Recommendations
For deep wells, test for:
- Standard panel (bacteria, nitrates, pH, hardness)
- Arsenic (especially if neighbors have found it)
- TDS (may be elevated)
- Fluoride (can be high in some deep water)
Deep Well Service Considerations
Pump Replacement Challenges
- Heavy equipment needed — More powerful rigs for deep pulls
- Longer pipe strings — 500+ feet of drop pipe
- Weight — Pump, pipe, and cable can weigh 500-1,000+ lbs
- Time — Deep pulls take longer, increasing labor cost
- Specialized crews — Not all companies work on deep wells
Service Cost Factors
| Service | 200-ft Well | 500-ft Well |
|---|---|---|
| Pump replacement | $1,500-$2,500 | $3,500-$6,000 |
| Motor replacement | $800-$1,500 | $1,500-$3,000 |
| Service call (troubleshooting) | $150-$300 | $200-$400 |
Extended Lifespan Strategies
Deep well pump replacements are expensive—extend pump life by:
- Quality installation — Proper sizing and components
- Clean power — Protect from surges and voltage issues
- Soft start or VFD — Reduces motor stress
- Proper pressure tank — Prevents short cycling
- Regular monitoring — Catch problems early
Deepening vs. New Well
If your existing well isn't deep enough, you may face a choice:
Deepening Existing Well
- Pros: Often cheaper than new well, uses existing infrastructure
- Cons: Not always possible (depends on casing), limited by existing diameter
- Cost: $50-$100 per additional foot plus new pump
Drilling New Well
- Pros: Start fresh, optimal design, can relocate
- Cons: Higher cost, need to abandon old well
- Cost: $40,000-$100,000+ for deep new well
When New Well Makes Sense
- Existing well casing is too narrow
- Casing is damaged or deteriorated
- Current location has geological problems
- Need significantly more water (wider casing)
Frequently Asked Questions
How deep can a residential well be?
Residential wells can be drilled to 1,000+ feet or even deeper in some cases, though 400-800 feet is typically the practical limit for most residential situations. In San Diego County, wells commonly range from 200-600 feet, with some mountainous or drought-affected areas requiring 800+ feet. Depth is limited primarily by drilling equipment capacity, pump technology, and cost—not by the availability of water at depth. Economic considerations usually determine practical limits more than technical ones.
How much does a 500-foot well cost?
A 500-foot well in San Diego County typically costs $40,000-$70,000 or more total, including drilling ($50-$100+ per foot depending on geology), steel casing for the full depth, a high-head submersible pump rated for the depth, electrical installation with proper wire sizing, and permits. Deep wells cost significantly more than shallow wells due to longer drilling time, specialized equipment, more casing material, and higher-capacity pumps capable of lifting water from depth. Rocky or difficult formations can push costs even higher.
Do deep wells have better water quality?
Generally yes. Deep wells access older, more protected water that has been naturally filtered through rock for years, decades, or even centuries. They're less susceptible to surface contamination, agricultural runoff, septic system influence, and seasonal variations. However, very deep water can have higher mineral content (harder water, higher TDS) due to longer contact time with rock, and some geological formations have naturally occurring contaminants like arsenic or fluoride at depth. Testing is always recommended.
What pump do I need for a 400+ foot well?
Wells over 400 feet require high-head submersible pumps specifically designed for deep settings. Standard residential pumps are typically rated to 300-400 feet; deeper wells need pumps with additional impeller stages and motors rated for greater depths. A 500-foot well might need a pump rated for 600+ feet to account for drawdown during pumping. Three-phase power is often recommended for deep well pumps (5+ HP) for better efficiency, cooler operation, and longer motor life. Proper sizing by a professional is essential.
Our Deep Well Services
Southern California Well Service specializes in deep well systems:
- Deep well drilling — Equipment rated for 800+ feet
- High-head pump installation — Proper sizing for deep settings
- Three-phase conversions — For efficiency on deep pumps
- Pump pulls and replacement — Rig capacity for deep wells
- Well deepening — When additional depth is needed
- Water testing — Including arsenic and deep-water parameters
Deep Well Questions?
We have the equipment and expertise for wells 400 feet and beyond.
Call (760) 440-8520Drilling | Pump service | Deep well expertise
Related: Well Drilling | Drilling Costs | Pump Sizing
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