SC By SCWS Team | February 2, 2026 | 11 min read
Understanding Well Yield Test Results
Just had your well tested and staring at a report full of numbers? Well yield test results can seem confusing, but understanding them is crucial—whether you're buying a property, troubleshooting water problems, or just curious about your well's health. This guide explains exactly what those numbers mean, how to know if your yield is adequate, and what options you have if it's not.
📊 Quick Reference: Is Your Yield Adequate?
- • 10+ GPM: Excellent — more than enough for most homes with irrigation
- • 5-10 GPM: Good — comfortable for typical family use
- • 3-5 GPM: Adequate — works well with proper management
- • 1-3 GPM: Marginal — may need storage tank
- • Less than 1 GPM: Low — requires storage system or well improvement
What Is a Well Yield Test?
A well yield test (also called a pump test, flow test, or production test) measures how much water your well can sustainably produce. The test determines the maximum rate at which you can pump water without depleting the well—expressed in gallons per minute (GPM) or gallons per hour (GPH).
This test is different from just seeing how fast water comes out of a hose. A true yield test:
- Runs the pump continuously for several hours (typically 4-24 hours)
- Monitors water level throughout the test
- Measures actual flow rate, not just pump capacity
- Determines sustainable yield, not just peak short-term flow
- Often includes recovery data after pumping stops
Key Terms on Your Test Report
Understanding the terminology helps you interpret your results:
| Term | What It Means | Why It Matters |
|---|---|---|
| GPM (Gallons Per Minute) | Flow rate the well can sustain | Primary indicator of well capacity |
| Static Water Level | Water level when pump is off | Shows available water column height |
| Pumping Water Level | Water level while pumping | Indicates aquifer responsiveness |
| Drawdown | Difference between static and pumping levels | How much the level drops during use |
| Specific Capacity | GPM per foot of drawdown | Well efficiency rating |
| Recovery Rate | How fast water level returns after pumping | Aquifer recharge capability |
How to Read Your Test Results: An Example
Let's walk through a typical well test report:
Sample Well Test Results
Well Depth: 320 feet
Static Water Level: 85 feet below surface
Test Duration: 4 hours
Pump Rate: 8 GPM
Pumping Water Level: 145 feet
Drawdown: 60 feet (145 - 85)
Specific Capacity: 0.13 GPM/ft
Recovery: 90% in 2 hours
What This Example Tells Us:
- Yield of 8 GPM: This is a good, adequate well for residential use
- 85 feet static level: There's 235 feet of water column above the well bottom (320 - 85)
- 60 feet drawdown: The water level drops 60 feet during pumping—significant but acceptable
- Specific capacity of 0.13: Average for fractured rock aquifers in Southern California
- Good recovery: The aquifer recharges well, indicating sustainable supply
Is Your Well Yield Adequate?
The real question isn't just "how much can my well produce?" but "is it enough for my needs?" Let's put the numbers in context:
Typical Household Water Use
🚿 Water Use by Activity
Shower
2-3 GPM for 8-10 minutes = 20-30 gallons
Toilet Flush
1.6-3.5 gallons per flush
Dishwasher
6-10 gallons per load
Washing Machine
15-40 gallons per load
Lawn Sprinkler
4-10 GPM while running
Person Per Day
50-100 gallons average
Converting GPM to Daily Capacity
Here's the math that puts yield in perspective:
💡 Daily Production Formula
GPM × 60 minutes × Hours of pumping = Gallons per day
Example: 5 GPM × 60 × 8 hours = 2,400 gallons per day
That's enough for a family of 4-6 with comfortable margin!
Even a "low" yield of 2 GPM can produce 2,880 gallons over 24 hours. The challenge isn't total production—it's matching peak demand. If you try to run two showers and a washing machine simultaneously, you might briefly exceed what a 2-3 GPM well can supply in real-time.
Yield Ratings Explained
Excellent (10+ GPM)
More than enough for large families, multiple bathrooms, and reasonable irrigation. Can handle simultaneous high-demand situations with ease.
Good (5-10 GPM)
Comfortable for typical family use. Can run multiple fixtures simultaneously. May need to stagger irrigation and heavy indoor use.
Adequate (3-5 GPM)
Works well with normal use patterns. Avoid running multiple high-demand fixtures at once. Consider low-flow fixtures. Adequate for most families.
Marginal (1-3 GPM)
Functional with water-conscious habits. May benefit from storage tank to buffer peak demand. Irrigation may need to be separate system or very limited.
Low (Less than 1 GPM)
Requires storage tank system. Well pumps into tank slowly; house draws from tank. Can work fine with proper setup. May want to explore yield improvement options.
Understanding Drawdown and Specific Capacity
Why Drawdown Matters
Drawdown—how far the water level drops while pumping—reveals important information about your well and aquifer:
- Small drawdown (under 20 feet): Indicates a highly productive aquifer that easily keeps up with pumping
- Moderate drawdown (20-80 feet): Normal for most wells—aquifer supplies water at a reasonable rate
- Large drawdown (80+ feet): Aquifer struggles to keep up; well may be near capacity or aquifer has limited transmissivity
Specific Capacity: The Efficiency Rating
Specific capacity (GPM per foot of drawdown) is perhaps the most useful number for comparing wells or tracking changes over time. Higher is better:
| Specific Capacity | Rating | Typical Formation |
|---|---|---|
| 0.5+ GPM/ft | Excellent | Highly fractured rock, gravel aquifer |
| 0.1-0.5 GPM/ft | Good | Moderately fractured granite, sandstone |
| 0.05-0.1 GPM/ft | Fair | Tight rock with limited fractures |
| Under 0.05 GPM/ft | Low | Very tight formation, may need improvement |
If your specific capacity declines over time (from tests years apart), it may indicate well deterioration—scale buildup, biofouling, or aquifer changes. This is valuable information for planning maintenance or well rehabilitation.
Types of Well Tests
Not all yield tests are equal. Understanding what type of test was performed helps you interpret results:
Short Pump Test (1-4 hours)
- Most common for real estate transactions
- Provides reasonable estimate of yield
- May overestimate yield if aquifer is at seasonal high
- Adequate for most purposes
Extended Pump Test (24-72 hours)
- More accurate, especially for low-yield wells
- Shows whether yield is truly sustainable
- Reveals wells that deplete with extended use
- Recommended for uncertain or marginal situations
Recovery Test
- Measures how quickly water level returns after pumping stops
- Indicates aquifer recharge capability
- Fast recovery = good aquifer connection
- Slow recovery = limited aquifer supply
⚠️ Test Timing Matters
Yield can vary seasonally—a test in wet spring may show 20% higher yield than the same well tested in dry fall. For the most conservative (safest) estimate, test during the driest time of year.
What If Your Yield Is Low?
A low yield doesn't necessarily mean a useless well. Here are your options:
Storage Tank System
For wells producing 1-3 GPM, a storage tank system often solves the problem economically:
- Large tank (1,000-2,500 gallons) accumulates water continuously
- Booster pump delivers stored water to house at normal pressure
- You have instant high-flow access to stored water
- Well replenishes tank slowly over time
- Cost: $3,000-$8,000 installed
Well Rehabilitation
If yield has declined from previous levels, rehabilitation may restore production:
- Chemical treatment dissolves scale and mineral buildup
- Mechanical cleaning removes sediment and debris
- Can restore 20-100% of lost yield in many cases
- Cost: $1,500-$5,000
Learn more about well rehabilitation costs and when it makes sense.
Hydrofracturing
For wells in hard rock (granite, basite), hydrofracturing can create new water pathways:
- High-pressure water is injected to open existing fractures
- Creates connection to additional water-bearing zones
- Success rate: 60-80% see meaningful improvement
- Cost: $2,500-$6,000
See our complete guide to hydrofracturing.
Well Deepening
If the water table has dropped or additional water zones exist deeper:
- Extend existing well to reach deeper aquifer zones
- Requires drilling rig and is not always possible
- Success depends on local geology
- Cost: $5,000-$15,000+
Learn about well deepening costs and considerations.
New Well
Sometimes a new well in a different location is the best option:
- Targets different aquifer zone or better location
- May be necessary if existing well is in poor condition
- Allows optimized design for your needs
- Cost: $15,000-$50,000+ (full turnkey)
Seasonal and Long-Term Yield Changes
Normal Seasonal Variation
Most wells experience some seasonal fluctuation:
- Spring (post-rain): Highest yield, highest static level
- Late summer/fall: Lowest yield, deepest static level
- Variation: Typically 10-30% between seasons
This is normal and expected. Your well system should be designed for the lower end of this range.
When to Be Concerned
These patterns suggest problems beyond normal variation:
Sudden Yield Drop
Pump problem, damaged casing, or aquifer issue—needs investigation
Progressive Multi-Year Decline
Scale buildup, biofouling, or regional aquifer depletion
Yield Drops Only During Drought
May indicate shallow aquifer vulnerable to dry conditions
Recovery Time Increasing
Aquifer connection degrading—well may need rehabilitation
Well Testing for Real Estate Transactions
If you're buying or selling property with a well, yield testing is essential:
For Buyers
- Always test before purchase: Don't rely solely on seller's claims or old reports
- Request extended test: 4 hours minimum; 24 hours for marginal wells
- Consider timing: Late summer testing gives conservative estimate
- Get professional opinion: Have results interpreted by a well professional
- Ask about history: Has the well ever run dry? Any repairs?
For Sellers
- Test proactively: Know what you're selling
- Address issues first: Low yield? Consider rehabilitation before listing
- Document maintenance: Records add value and buyer confidence
- Disclose honestly: Yield problems discovered later create bigger problems
Frequently Asked Questions
What is a good well yield?
For a typical residential home, 5 GPM (gallons per minute) is generally considered adequate for most needs. However, 3-5 GPM can work with proper management, and 10+ GPM provides comfortable margin for larger families or irrigation. Less than 3 GPM may require storage tanks or other solutions.
What does GPM mean on a well test?
GPM stands for Gallons Per Minute—the rate at which your well can sustainably produce water. A well test measures this by pumping water at a steady rate and monitoring water level. The sustainable yield is the GPM rate the well can maintain without the water level dropping excessively.
How is a well yield test performed?
A well yield test involves pumping the well at a measured rate while monitoring the water level. Typically, the pump runs for 4-24 hours while technicians record static water level, pumping water level, drawdown, and recovery rate. Results show sustainable yield in GPM and specific capacity.
What if my well yield test shows low production?
Low well yield options include: well rehabilitation to clean and restore production, installing storage tanks to accumulate water between uses, hydrofracturing to create new water pathways in rock, deepening the well to reach more water, or drilling a new well. A professional assessment determines the best approach.
How much water does a household use per day?
Average household water use is 50-100 gallons per person per day. A family of four uses approximately 200-400 gallons daily. Peak demand (morning/evening) may require 5-10 GPM briefly, but total daily use spread over 24 hours means even low-yield wells can work with storage.
Does well yield change over time?
Yes, well yield can change. Seasonal fluctuations are normal—wells often produce less in late summer after dry periods. Long-term decline may indicate scale buildup, biofouling, or regional aquifer changes. Sudden drops suggest mechanical problems or specific well issues that need investigation.
Need a Professional Well Yield Test?
Whether you're buying property, troubleshooting low water, or want to know your well's true capacity, we perform comprehensive yield tests throughout San Diego County. Our detailed reports include interpretation and recommendations specific to your situation.
