How to Find a Leak in Underground Pool Plumbing

Is your pool losing water faster than usual? You’re not alone—leaks in underground pool plumbing are a common but often hidden issue that can waste thousands of gallons of water and inflate your utility bills. Knowing how to find a leak in underground pool plumbing early can save you time, money, and major headaches down the line. In this guide, we’ll walk you through proven, DIY-friendly methods to detect and confirm leaks—plus when it’s time to call a pro.

Why Underground Pool Leaks Are Hard to Detect

Unlike surface-level leaks (like a cracked tile or a loose fitting), underground plumbing runs beneath concrete, decking, or soil—making visual inspection impossible. According to the U.S. Department of Energy, a small 1/16-inch pool leak can waste up to 7,000 gallons of water per month. That’s not just costly—it’s environmentally unsustainable.

Because these leaks are concealed, they often go unnoticed until water loss becomes obvious or the surrounding ground becomes soggy. Early detection is key, and fortunately, you don’t need to be a plumber to start investigating.

Step-by-Step: How to Confirm You Have a Leak

Before assuming you have an underground leak, rule out evaporation and splash-out:

1. Perform the Bucket Test
   • Fill a bucket with pool water to within 1 inch of the top.
   • Place it on the pool step so the water level inside matches the pool’s water level.
   • Mark both water levels with tape.
   • Wait 24–48 hours (with the pump running normally).
   Result: If the pool water drops significantly more than the bucket water, you likely have a leak.

💡 Tip: Do this test during calm, non-windy weather for accuracy.

Common Signs of an Underground Pool Plumbing Leak

Watch for these red flags:

• Unexplained water loss (more than ¼ inch per day)
• Wet or mushy spots in your yard near plumbing lines
• Air bubbles in the return jets (indicates suction-side leak)
• Higher-than-normal water bills
• Pool pump losing prime repeatedly
• Cracks in the pool deck (caused by eroded soil from leaking water)

If you notice two or more of these, it’s time to dig deeper—figuratively and sometimes literally.

How to Locate the Leak: DIY Methods That Work

1. Check the Equipment Pad First

Start above ground. Leaks often originate at valves, filters, or pump unions—not underground. Inspect all visible PVC joints, O-rings, and connections for moisture, corrosion, or drips.

⚠️ Many homeowners assume the leak is underground when it’s actually at the equipment pad—saving you a costly excavation.

2. Isolate the Suction vs. Pressure Side

Your plumbing has two main sections:

• Suction side: From skimmer/main drain → pump
• Pressure side: From pump → filter → return jets

Test:

• Turn off the pump and plug the skimmer and main drain lines.
• Fill the pool to normal level.
• Wait 24 hours.
• If water level drops: Leak is likely on the pressure side (underground return lines).
• If water holds: Leak is on the suction side (could be underground or at the skimmer).

3. Use Dye Testing for Precision

For suspected suction-side leaks (e.g., around skimmer):

• With the pump off, add food-grade dye near the skimmer throat or pipe joints.
• Turn the pump on briefly.
• If dye gets sucked into a crack or joint—bingo! That’s your leak.

📌 Note: Dye testing only works on accessible areas. For buried lines, move to pressure testing.

4. Pressure Test the Lines (Best for Confirmation)

This is the gold standard for confirming underground leaks. You’ll need a pressurized air or water test kit (available for rent or hire a pro).

Process:

• Shut off all valves.
• Disconnect lines at the equipment pad.
• Seal one end of the pipe.
• Inject air or water at 15–20 PSI (standard pool operating pressure).
• Monitor pressure for 10–15 minutes.
• Pressure drops? → Leak confirmed.
• Stable pressure? → No leak in that line.

🔧 Pro Tip: Test suction and return lines separately. Return lines are more prone to underground leaks due to constant pressure.

For more on plumbing pressure dynamics, see Wikipedia’s overview of fluid pressure systems .

When to Call a Professional Leak Detection Service

While DIY methods work for basic diagnostics, underground leaks often require specialized tools like:

• Acoustic listening devices (detect water escaping under pressure)
• Thermal imaging cameras (spot temperature differences from water flow)
• Tracer gas injection (helium or hydrogen mixed with nitrogen to pinpoint leaks)

According to the Association of Pool & Spa Professionals (APSP), 85% of underground leaks are found within 2 feet of fittings or directional changes—but locating them without excavation requires expertise.

Call a pro if:

• You’ve confirmed a leak but can’t locate it
• Your yard shows sinkholes or structural damage
• You’re uncomfortable working with pressurized systems

Most certified leak detection services charge $200–$500, far less than unnecessary excavation ($2,000+).

Pros vs. Cons: DIY vs. Professional Leak Detection

Preventing Future Underground Leaks

Once fixed, protect your investment:

• Winterize properly: Drain lines in freezing climates to prevent pipe bursts.
• Avoid ground shifting: Don’t plant large trees near plumbing lines—their roots can crack pipes.
• Schedule annual inspections: A quick pressure test every spring catches issues early.
• Use quality materials: Schedule repairs with Schedule 40 PVC (not thin-walled alternatives).

FAQ: How to Find a Leak in Underground Pool Plumbing

Q1: Can a pool leak underground and not show on the surface?

A: Yes. Water can seep into surrounding soil without surfacing—especially in sandy or well-draining yards. That’s why pressure testing is essential.

Q2: How much does it cost to fix an underground pool leak?

A: Repair costs range from $500 to $3,000, depending on depth, location, and whether excavation is needed. Early detection keeps costs low.

Q3: Will a pool leak cause foundation damage?

A: Potentially. Continuous water leakage can erode soil under patios, decks, or even your home’s foundation. Address leaks promptly.

Q4: Can I use my pool while searching for a leak?

A: Yes, but avoid running the pump 24/7 during testing (e.g., bucket test). Normal usage is fine unless you see major water loss.

Q5: Do pool leak detection kits work?

A: Basic kits (dye, pressure gauges) help confirm leaks but can’t pinpoint underground locations. They’re great for initial screening.

Q6: How long does leak detection take?

A: DIY tests: 1–2 days. Professional services: Often completed in under 2 hours with modern equipment.

Conclusion

Learning how to find a leak in underground pool plumbing empowers you to act fast, conserve water, and avoid expensive damage. While not every leak requires a pro, knowing the signs—and when to call for help—saves time and money. Start with simple tests like the bucket method, isolate your plumbing sides, and don’t ignore subtle clues like soggy grass or air in your jets.

If this guide helped you, share it with fellow pool owners on Facebook, Pinterest, or Nextdoor! A little knowledge goes a long way in keeping backyard oases safe, efficient, and leak-free.

Stay dry, save water, and swim on! 💦