Well Deepening vs. Drilling a New Well
Published February 1, 2026 | 13 min read
When your well isn't producing enough water, you have two primary options: deepen the existing well or drill a completely new one. Each has distinct advantages, costs, and risks. This guide helps you understand both options so you can make an informed decision that protects your investment and solves your water problems.
Understanding Your Options
Before diving into the comparison, let's clearly define what each option involves:
Well Deepening: What It Is
Well deepening involves drilling deeper through the bottom of your existing well to reach additional water-bearing formations. The process:
- Pull the existing pump and drop pipe
- Lower a drill bit through the existing casing
- Drill into new rock/formation below current depth
- Install a smaller-diameter "liner" casing in the new section
- Develop the new section to maximize flow
- Reinstall the pump (often deeper than before)
The new section will have a smaller diameter than the original well because the drill bit must fit inside the existing casing.
New Well: What It Is
A new well means drilling a completely separate well in a new location. This involves:
- Site evaluation and permit application
- Drilling from the surface to target depth
- Installing full-diameter casing and screen
- Development and flow testing
- Pump installation
- Connecting to your water system
- Properly abandoning the old well (required by law)
Cost Comparison
Cost is often the primary factor in this decision. Here's what to expect in Southern California:
Well Deepening Costs
- Mobilization and setup: $1,500-$3,000
- Pull existing pump: $500-$1,500
- Drilling (per foot): $40-$100/ft (100-200 ft typical)
- Liner casing: $15-$30/ft installed
- Development: $1,000-$3,000
- Pump reinstallation (deeper): $1,500-$4,000
- Total typical cost: $10,000-$30,000
New Well Costs
- Permitting: $500-$1,500
- Mobilization and setup: $2,000-$4,000
- Drilling (per foot): $40-$80/ft
- Casing and screen: $15-$40/ft installed
- Development and testing: $1,500-$4,000
- Pump and installation: $2,000-$5,000
- Connection to house: $1,000-$3,000
- Old well abandonment: $2,000-$5,000
- Total typical cost: $15,000-$50,000+
The Hidden Cost Factor
Deepening looks cheaper upfront, but consider: if deepening fails to find adequate water, you've spent $15,000-$25,000 and still need a new well. A new well has higher upfront cost but higher certainty of success when properly sited.
When to Deepen Your Existing Well
Well deepening makes sense when specific conditions are met:
Good Candidates for Deepening
- Existing casing is in good condition: No severe corrosion, holes, or collapse
- Adequate casing diameter: 6" or larger preferred (smaller limits options)
- Known deeper water: Geological data or neighbor wells confirm water at greater depth
- Compatible geology: Drillable formation below current depth
- No contamination issues: Going deeper won't draw from contaminated zones
- Recent well: Less than 20-25 years old with minimal structural concerns
Ideal Deepening Scenarios
- Well was drilled during wet years and didn't reach deep enough for drought conditions
- Water table has dropped regionally but deeper aquifers still hold water
- Original driller stopped drilling before reaching the best water zone
- You need modest increase (doubling yield, not 10x increase)
- Hydrogeological evaluation confirms favorable conditions
When to Drill a New Well
A new well is the better choice in these situations:
New Well Is Better When
- Existing casing is compromised: Holes, severe corrosion, or structural damage
- Small casing diameter: 4" or smaller limits deepening options
- Contamination problems: Current location has ongoing water quality issues
- Uncertain geology: No evidence of deeper water at current location
- Better location available: Different spot has more favorable geology
- Significantly more water needed: Current well/location can't support demand
- Old well construction: Poorly built well that doesn't meet current standards
- Previous deepening failed: Already tried and didn't find adequate water
New Well Advantages
- Optimal location: Site it for best geology, not where old well happened to be
- Full diameter: No narrowing sections from liner installations
- Modern construction: Current codes, materials, and techniques
- Full lifespan: 30-50+ years of service ahead
- Higher success rate: 90%+ with proper evaluation vs. uncertain deepening
Pros and Cons: Side-by-Side Comparison
Well Deepening
Pros
- Lower upfront cost (30-60% less)
- Faster process (no new permits needed in most cases)
- No new site disturbance
- Uses existing infrastructure
- No well abandonment required (yet)
Cons
- No guarantee of finding water
- Limited by existing casing condition and size
- Smaller diameter reduces future options
- Doesn't address structural problems
- May be throwing money at a dying well
New Well
Pros
- Higher success rate (90%+)
- Optimal location selection
- Full casing diameter throughout
- Modern construction and materials
- Full expected lifespan (30-50 years)
- Clean slate—no inherited problems
Cons
- Higher upfront cost
- Permit process (2-4 weeks)
- Must abandon old well (additional cost)
- More property disruption
- Still has drilling uncertainty
Success Rates and Risk Assessment
Understanding the risk of each option helps you make a more informed decision:
Deepening Success Rates
Success rates for well deepening vary significantly based on conditions:
- Favorable conditions (known deep water, good casing): 70-85% success
- Moderate conditions (uncertain geology): 50-70% success
- Unfavorable conditions (no data, older well): 30-50% success
"Success" means achieving meaningful improvement in yield—not necessarily solving all problems.
New Well Success Rates
New well success rates are generally higher, especially with proper evaluation:
- With hydrogeological evaluation: 90-95% success
- Based on neighbor wells only: 75-85% success
- Challenging areas (hard rock, etc.): 60-80% success
"Success" means finding adequate water for the intended use at a reasonable cost.
The Decision Framework
Use this framework to guide your decision:
Step 1: Assess Your Current Well
Before deciding, get professional evaluation of your existing well:
- Video inspection: Reveals casing condition, diameter, and any problems
- Flow test: Documents current yield vs. original capacity
- Water quality test: Identifies any contamination issues
- Well log review: Shows original drilling data and formations
Step 2: Understand the Geology
What's below your current well depth?
- Review neighbor well logs: What did deeper drilling find?
- Consult geological maps: What formations exist at depth?
- Hydrogeological evaluation: Professional assessment of water probability
Step 3: Calculate True Costs
Consider more than just upfront expense:
- If deepening fails: You've spent money and still need a new well
- Remaining lifespan: An older deepened well may need replacement sooner
- Future restrictions: Smaller liner limits future pump/repair options
- Water quality: Deeper water may require more treatment
Step 4: Make Your Decision
Choose Deepening If:
- Casing is in good condition (video confirms)
- Evidence suggests deeper water exists
- Well is relatively new (under 20 years)
- Cost savings are meaningful to your budget
- You need modest improvement, not dramatic increase
Choose New Well If:
- Current well has structural problems
- Uncertain whether deeper water exists at current location
- Water quality problems persist
- You need significantly more water
- Well is old (25+ years) with ongoing issues
- Better drilling location is available
Special Considerations for Southern California
Regional factors affect the deepening vs. new well decision:
Fractured Rock Aquifers
Much of San Diego County relies on fractured bedrock aquifers. Water exists in rock fractures, not uniform layers. This means:
- Deeper drilling doesn't guarantee more fractures
- Neighboring wells may have very different results
- Hydrofracturing may be an alternative to deepening
- New well location may hit completely different fracture systems
Deep Well Requirements
Many areas require deep wells (300-600+ feet) due to regional water table conditions. If your well is already 400 feet and needs deepening, consider:
- Additional 100-200 feet adds significant cost
- Pump depth increases and costs rise
- A new well at the same total depth may cost similar to deepening
Permit Considerations
In some areas (like adjudicated basins), new wells require specific permits and may face restrictions. Deepening an existing permitted well may be simpler administratively.
What If You're Still Uncertain?
If the decision isn't clear, consider these approaches:
Get a Hydrogeological Evaluation
A professional hydrogeologist can review your well, local geology, and neighbor data to give an informed recommendation. Cost: $500-$2,000 but can save you from expensive mistakes.
Start with Rehabilitation
If your well might just be clogged or scaled, try rehabilitation first. If that restores adequate yield at $5,000-$10,000, you've avoided both deepening and new well costs.
Consider Hydrofracturing
For bedrock wells, hydrofracturing ($8,000-$15,000) may open new fractures without drilling deeper. It's a middle-ground option between rehabilitation and deepening.
Frequently Asked Questions
How much does it cost to deepen a well vs drill a new one?
Well deepening typically costs $10,000-$30,000 depending on depth added and conditions. A new well in Southern California costs $15,000-$50,000+ depending on total depth required. Deepening is usually 30-60% less expensive upfront, but consider that a new well provides a complete fresh start with modern construction and full expected lifespan.
Can any well be deepened?
No. Well deepening requires: existing casing in good condition, compatible geology (drillable rock below current depth), adequate casing diameter for the drill bit, and favorable hydrogeological conditions (water available at greater depth). Old wells with corroded casing, small diameters, or those already drilled to bedrock may not be candidates for deepening.
Is well deepening or a new well more likely to succeed?
A new well has higher success rates (90%+ with proper site evaluation) because you can choose optimal location and drill through the best formations. Deepening success depends heavily on whether there's actually more water below your current depth. Hydrogeological evaluation helps predict outcomes for both options.
How deep can a well be deepened?
Wells can typically be deepened 50-300 additional feet, limited by: existing casing condition, diameter constraints (deeper sections must be smaller), geology (drilling method must match rock type), and practical economics. At some point, deepening becomes more expensive than drilling new.
What if well deepening doesn't find more water?
Unfortunately, you'll have paid for the drilling without getting results. This is the primary risk of deepening—there's no guarantee of finding water. However, a thorough hydrogeological evaluation beforehand can assess the probability of success. If evaluation suggests low probability, a new well in a better location may be the smarter investment.
Need Help Deciding?
We'll evaluate your well, review local geology, and give you an honest recommendation—deepening, new well, or another option. Our goal is solving your water problems the most cost-effective way, not selling you the most expensive solution.