What Is Actually Happening Under Your Pool?
Most Toronto homeowners give very little thought to what is buried beneath their pool deck until something goes wrong. The pump hums, water circulates, chemicals do their job, and everything looks fine from the surface. But underneath the concrete, interlock, or natural stone sits a network of pipes, fittings, and valves that the entire system depends on. When that network develops a problem, even a small one, the consequences can range from steadily climbing water bills to significant structural damage if the issue is left alone long enough.
Understanding how your inground pool’s plumbing works, and where it is most likely to fail, is one of the most practical things a pool owner can know. This guide covers the main components of a pool plumbing system, the materials typically used in Toronto builds, and the failure modes that show up most often in our climate. For a deeper look at how these systems are installed from the ground up, see our step-by-step guide to pool construction in Toronto.
The Two Sides of Your Pool’s Plumbing System
Every inground pool plumbing system is divided into two distinct circuits by the pump: the suction side and the pressure side. Keeping these two sides straight will help you interpret any symptoms you notice and communicate them clearly to a pool professional.
The Suction Side
The suction side includes every pipe and fitting between the water inlets and the pump intake. Water enters the system through two main points: the skimmer (or skimmers, depending on pool size) and the main drain at the bottom of the pool. Both of these lines run underground to the equipment pad and connect to the pump’s inlet port.
Because the pump creates negative pressure on this side of the system, suction-side leaks do not push water out into the surrounding soil the way pressure-side leaks do. Instead, they pull air in through the crack or loose fitting, which then gets expelled through the return jets as bubbles. Suction-side problems tend to show up as air in the system, a pump that struggles to prime, or gurgling sounds at the skimmer.
The Pressure Side
Once water passes through the pump, it enters the pressure side of the system. From the pump outlet, it flows through the filter, then through the heater if one is installed, and finally returns to the pool through the return inlets set into the pool walls. All of these components and the pipes connecting them operate under positive pressure whenever the pump is running.
Pressure-side leaks push water outward through the breach. These are often the leaks that cause soggy ground near the equipment pad, sinkholes beneath the pool deck, or visibly saturated soil along the pipe runs. Because the pump is actively forcing water through the crack, pressure-side leaks tend to cause faster water loss than suction-side ones.
Key Components in the Plumbing System
Skimmer Lines
Skimmers are the rectangular inlets built into the pool wall just below the waterline. Each skimmer connects to an underground pipe that runs to the pump. A typical residential pool in Toronto has one or two skimmers. The skimmer housing itself sits in the pool shell, and the connecting pipe transitions from the shell to the buried run beneath the deck. This transition point is a common location for leaks, particularly as the pool shell and the surrounding soil shift over time.
Main Drain Line
The main drain sits at the deepest point of the pool floor. Its primary function is to provide an even draw across the bottom of the pool to support circulation, and in some systems it also acts as a safety drain. The main drain line runs straight down through the pool floor and then underground to the pump. Because this pipe transitions from the pool floor into the surrounding soil, it is particularly susceptible to movement-related stress at the penetration point.
Return Lines
Return lines carry filtered, treated water back into the pool from the pressure side of the system. The inlets are typically mounted flush with the pool wall below the waterline. Like the skimmer lines, return lines run underground from the equipment pad back to the pool shell. The fittings where they pass through the shell wall are a common location for slow seeping leaks as the shell ages and experiences seasonal movement.
Equipment Pad Components
The pump, filter, heater, and any additional equipment (salt cell, automation valves, chlorinator) sit on the equipment pad above ground. The pipes connecting these components are above-grade and visible, making leaks here easier to detect and repair. Unions, valves, and threaded fittings on the equipment pad do loosen over time and are worth checking each spring as part of your pool opening routine.
Pipe Materials: What Is Used and Why It Matters
The vast majority of inground pool plumbing in Canada uses rigid Schedule 40 PVC pipe. Schedule 40 refers to the pipe’s wall thickness rating. For pool applications, it is the appropriate choice for underground runs because it handles the operating pressures involved, resists chemical exposure from pool water, and does not corrode.
Some contractors use flexible PVC pipe for above-ground connections at the equipment pad, where it makes routing around pumps and filters easier. Flexible PVC is a legitimate choice for above-ground use, but it should not be used for underground runs. It is more susceptible to damage from insect activity and from chlorine permeation over time. If an older pool’s underground plumbing was installed with flex PVC, that is worth knowing when assessing the system’s condition.
Fittings and joints are connected using PVC solvent cement, which chemically bonds the pipe and fitting into a single piece when applied correctly. The strength and longevity of every joint in the system depends on the quality of that bond at installation and on how much stress the joint has experienced since.
How Pool Plumbing Fails: The Most Common Causes
Freeze-Thaw Damage
In Toronto, this is the leading cause of pool plumbing problems. When a pool is not properly winterized and water remains in the underground lines, that water expands as it freezes. PVC cannot flex to accommodate the expansion and the pipe cracks. Even in properly winterized pools, ground frost creates pressure on buried pipe runs as the soil contracts and expands through the season. Joints that have been through 15 or 20 freeze-thaw cycles are under meaningfully more stress than they were when the pool was new.
Joint and Fitting Failure
The glued joints between pipe sections and fittings are the most common point of failure in any pool plumbing system. Solvent cement has a finite lifespan, and repeated pressure cycling, chemical exposure, and movement gradually degrade the bond. In a typical pool, the pump cycles on and off thousands of times per season. Each cycle creates a brief pressure surge through the system. Over a decade or more, these small stresses accumulate at the weakest points in the network, which are almost always the joints.
Tree Root Intrusion
Roots from trees and large shrubs seek moisture and can grow toward pool plumbing lines, especially if there is any seeping moisture nearby. Roots do not break pipes directly in most cases, but they can displace the surrounding soil in ways that create lateral stress on buried pipe runs and joints. Pools with mature trees nearby, particularly willows, silver maples, and other aggressive-rooted species common in Toronto neighborhoods, are more likely to experience this type of pressure over time.
Soil Movement and Settlement
Toronto’s clay-heavy soils expand when wet and contract when dry. Over a full season, the soil around your pool’s underground plumbing can shift noticeably. Pipes are rigid, but soil is not. When the ground moves around a buried pipe, it can create bending stress at points where the pipe transitions direction or connects to a fitting. Longer underground runs across unstable fill or clay-heavy subsoil are more vulnerable to this type of stress.
Age and Material Degradation
PVC pipe does not last indefinitely. Ultraviolet exposure degrades above-ground sections over time, though above-ground runs are usually protected or shaded at a well-maintained equipment pad. Underground sections are protected from UV but are subject to chemical exposure from the pool water moving through them over decades. Most pool plumbing systems in good condition will last 20 to 30 years before age-related issues become common. Pools built in the early 2000s and before are at the age where a proactive plumbing assessment is worth considering.
| Failure Cause | Most Common Location | Symptom |
|---|---|---|
| Freeze-thaw damage | Underground suction or return lines | Water loss, air in system at spring opening |
| Joint failure | Any glued fitting, especially bends | Slow leak, soggy soil, gradual water loss |
| Tree root pressure | Long underground runs near trees | Cracked pipe, persistent slow leak |
| Soil movement | Pipe transitions and direction changes | Cracking at fittings, deck settling above |
| Material aging | Older above-ground or exposed runs | Brittle pipe, hairline cracks, fitting loosening |
| Equipment pad fittings | Unions, valves, threaded connections | Visible drips, water pooling at equipment pad |
When Plumbing Problems Become Bigger Issues
A slow plumbing leak that goes unaddressed does not stay small. Water escaping underground follows the path of least resistance through the soil, and over a full season it can erode the substrate beneath your pool deck, create voids, and cause settling or cracking of the deck surface above. In worse cases, a sustained leak near the pool shell itself can undermine the structural support of the pool walls.
This is why a plumbing problem caught early, when it shows up as air bubbles or a slightly elevated water top-up frequency, is far less disruptive to repair than one discovered after visible deck damage or a pump running dry repeatedly. An annual check of the plumbing system at spring opening, including a visual inspection of all above-ground fittings and a quick eye on water level behavior over the first week, is one of the most worthwhile maintenance habits a pool owner in Toronto can build. Our inground pool maintenance guide covers the full seasonal routine in detail.
If your assessment points to significant plumbing damage, it is worth considering whether a broader pool restoration is the right approach rather than addressing each plumbing issue in isolation. Our guide to pool restoration in Toronto explains the range of work that typically falls under a restoration project and how to evaluate the right scope for your pool’s condition and age.
When to Call a Professional
Some above-ground equipment pad repairs, such as tightening a union, replacing a valve, or re-gluing an exposed fitting, are manageable for a mechanically capable homeowner. Underground plumbing repairs are a different matter entirely. Locating an underground leak accurately requires pressure-testing equipment and, in many cases, electronic listening devices. Getting it wrong means unnecessary excavation or missing the actual breach location entirely.
If you are seeing any of the symptoms described in this guide and the bucket test points to a plumbing-side leak, the right next step is a professional leak detection assessment before any work begins. Accurate diagnosis saves time, money, and disruption to your landscaping and deck.
At Destination Pools and Landscaping, we work with Toronto homeowners to assess pool plumbing systems, diagnose leaks, and carry out the repairs needed to get pools running properly and keep them that way. If you are planning a new inground pool installation, we can also walk you through how the plumbing system will be designed and laid out for your specific site and pool configuration.
Frequently Asked Questions
What type of pipe is used in inground pool plumbing?
The industry standard for inground pool plumbing in Canada is rigid Schedule 40 PVC pipe. It is rated for the operating pressures of a pool system, resistant to the chemicals present in pool water, and does not corrode. Joints and fittings are connected using PVC solvent cement. Above-ground connections at the equipment pad sometimes use flexible PVC for ease of routing, but rigid Schedule 40 is the correct choice for all underground runs.
How long does pool plumbing typically last?
A well-installed pool plumbing system using rigid Schedule 40 PVC can last 20 to 30 years before age-related issues become common. In Toronto’s climate, the freeze-thaw cycle accelerates wear on joints and fittings compared to pools in warmer regions. Pools that are 15 years or older and have never had a formal plumbing assessment are good candidates for a proactive inspection at spring opening.
Can I repair a pool plumbing leak myself?
Above-ground fittings at the equipment pad are sometimes manageable for a mechanically experienced homeowner. Underground plumbing repairs are not. Accurately locating a buried leak requires pressure-testing equipment and sometimes electronic listening devices. Excavating to the wrong location wastes time and money and damages your landscaping or deck unnecessarily. Underground pool pipe repairs should be handled by a qualified pool contractor.
What happens if a pool plumbing leak is left alone?
An unaddressed leak will gradually erode the soil supporting your pool deck, potentially creating voids that cause cracking and settling of the deck surface. Water loss compounds over time, increasing your municipal water costs throughout the season. In more serious cases, sustained leaks near the pool shell can undermine structural support for the pool walls. Early detection and repair is always significantly less disruptive and costly than dealing with the downstream damage.
Does a pool plumbing overhaul make sense for an older pool?
For pools that are 20 or more years old and showing repeated plumbing issues, a proactive assessment of the full underground system can make more financial sense than addressing individual leaks one at a time. Combining a plumbing overhaul with other restoration work, such as resurfacing the pool shell or updating the equipment, often reduces the total disruption compared to scheduling separate projects over multiple seasons.
Ready to Assess Your Pool’s Plumbing Health?
Whether you are troubleshooting a specific symptom or want a professional eye on your pool’s plumbing before a problem develops, Destination Pools and Landscaping is here to help. We work with Toronto homeowners across every stage of pool ownership, from new installations to full restorations, and everything in between.
Contact us to book a consultation. We will assess your pool’s current condition, explain what we find in plain language, and help you decide on the right path forward, whether that is a targeted repair or a more comprehensive restoration of your entire outdoor space.
