Leaving an inground pool empty is a scenario every pool owner eventually contemplates, whether during a sale, a long renovation, or to address persistent maintenance issues. The immediate assumption might be that draining the water is a simple solution, but the reality is far more complex. An empty inground pool is a structurally vulnerable pool, subject to a range of physical forces and environmental factors that can cause catastrophic and expensive damage. Understanding the specific risks associated with an emptied shell is the critical first step in making a responsible decision.
Understanding Pool Wall Pressure and Hydrostatic Force
The most significant danger to an empty inground pool is the sudden and immense pressure exerted on its walls and floor. For decades, your pool was designed as a water-filled vessel, where the surrounding groundwater and the water itself exert an outward push, known as hydrostatic pressure. This pressure is constantly counteracted by the weight of the pool water holding the structure inward. When you drain the pool, you remove that balancing force, leaving the walls completely susceptible to the immense lateral force of the groundwater pressing against them.
The Risk of Pop-Out and Wall Collapse
In areas with a high water table, this unbalanced force can be strong enough to cause the pool walls to bow outward, a phenomenon often called "pop-out." Concrete and gunite pools are particularly vulnerable, as the curing process can create microscopic hairline fractures that widen under stress. These minor flaws become pressure points where the structural integrity fails. Vinyl and fiberglass pools can also be compromised, with panels being pushed out of alignment or even rupturing under the strain. The result is a structural failure that can render the pool shell irreparable and collapse, turning a maintenance issue into a complete demolition project.
| Pool Type | Primary Risk When Empty | Severity |
|---|---|---|
| Gunite / Concrete | Wall blow-out, hairline cracks widening | High - Often leads to total structural failure |
| Vinyl Liner | Panel deformation, liner wrinkling or tearing | Medium - Significant damage requiring liner replacement |
| Fiberglass | Surface cracking, whole shell deformation | High - Risk of permanent creasing and weakness |
The Subtle Enemy: Groundwater and Soil Pressure
Even if your property doesn't have a visible creek or pond nearby, the soil beneath your pool is saturated with moisture. This groundwater is in constant motion, and its pressure fluctuates with rainfall, drought cycles, and seasonal changes. An empty pool creates a void that this groundwater will attempt to fill. This can lead to the soil underneath the pool's footer swelling, a process known as heaving. This heaving can lift the entire pool structure out of level, causing misalignment that is incredibly difficult and costly to fix. The pressure isn't static; it's a dynamic, relentless force that an empty pool is ill-equipped to handle.
Drainage Systems and The Need for Equalization
Professional pool contractors are acutely aware of these risks and adhere to strict engineering standards for a reason. The industry standard practice when a pool must be drained is not simply to open a drain and let the water go. It involves installing a hydrostatic relief valve or a complex system of gravel drains around the pool's perimeter. These systems are designed to allow groundwater to enter the pool shell in a controlled manner, equalizing the pressure and preventing the violent upward force that causes blow-outs. If your pool was drained without such a system in place, you are effectively playing a dangerous game of structural roulette.
Material Degradation and Long-Term Consequences
Beyond the immediate risk of collapse, leaving a pool empty for an extended period initiates a cascade of material degradation. The concrete or plaster surface is designed to be submerged. When exposed to air, the surface can dry out and "calcine," becoming brittle and prone to chipping. Sunlight and lack of water can cause the finish to craze and crack. Metal components, such as ladders, screws, and the coping, are exposed to oxygen and moisture in a way that accelerates rust and corrosion. When you eventually decide to refill the pool, you may be looking at extensive resurfacing and replacement of corroded parts, negating any initial savings from the draining process.
The Practical and Environmental Considerations
Finally, the decision to leave an inground pool empty is fraught with practical and environmental hurdles. Disposing of thousands of gallons of water is often restricted by local water conservation ordinances, and the cost to refill it can be substantial. Refilling a pool also needs to be done slowly and strategically to avoid further stressing the structure, a process that requires patience and planning. From a safety perspective, an empty pool is a severe liability. It presents a deep, hidden trench that is invisible and incredibly dangerous to children, pets, and even trespassers. For these reasons, industry experts and structural engineers universally advise against completely draining an inground pool unless it is an absolute last resort, and then only when done with professional guidance and appropriate pressure-relief measures in place.
