Most pools can safely remain empty for 1-2 weeks, but inground concrete pools face structural risks after this period due to hydrostatic pressure. Above ground pools can stay empty longer but may suffer liner damage.
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Before determining how long your pool can stay empty, we need to assess several critical factors that affect safety duration. The type of pool construction, local groundwater conditions, weather patterns, and reason for emptying all play crucial roles in determining safe timeframes.
The most important diagnostic question is: what type of pool do you have? Inground concrete/plaster pools face the highest risk when empty, while vinyl liner and fiberglass pools have different concerns. Above ground pools generally handle being empty much better than any inground option.
Maximum safe duration: 1-2 weeks
Concrete pools face the greatest risk when empty due to hydrostatic pressure from groundwater. When your pool is full, the water weight counteracts upward pressure from groundwater beneath the pool. Once empty, this pressure can cause the pool shell to literally pop out of the ground or crack severely.
Signs of hydrostatic pressure problems include:
Maximum safe duration: 3-4 weeks
Vinyl liner pools can typically stay empty longer because the liner isn't structural. However, extended emptiness causes liner shrinkage, making refitting extremely difficult or impossible. UV exposure also degrades vinyl rapidly.
Maximum safe duration: 1-2 weeks
Like concrete pools, fiberglass shells can pop out due to hydrostatic pressure. The lightweight nature of fiberglass actually makes them more susceptible to ground movement when empty.
Maximum safe duration: Several months
Above ground pools handle being empty much better since they're not fighting groundwater pressure. Main concerns are liner shrinkage and UV damage to pool walls.
If you live in an area with high groundwater (near lakes, rivers, or naturally wet soil), reduce all timeframes by 50%. These conditions create much higher hydrostatic pressure risks. You can identify high groundwater areas by:
Rainy seasons dramatically reduce safe empty time. Heavy rainfall increases groundwater levels and hydrostatic pressure. If significant rain is forecast, either refill immediately or install a hydrostatic relief valve system.
Extreme heat also accelerates liner damage and increases evaporation from surrounding soil, potentially causing ground settling around the pool.
For pools that must stay empty longer than recommended timeframes, install hydrostatic relief valves in the main drain. These valves automatically open when groundwater pressure builds up, allowing water to enter the pool and equalize pressure. This solution works for concrete and fiberglass pools but requires professional installation.
Instead of completely emptying, maintain 12-18 inches of water in the shallow end. This provides enough weight to counteract most hydrostatic pressure while still allowing major repairs or cleaning. Add 1 gallon of liquid chlorine per 1,000 gallons of remaining water weekly to prevent algae growth.
Install a monitoring well near your pool to track groundwater levels. If groundwater rises to within 2 feet of your pool floor, refill immediately regardless of your original timeline.
If you notice any signs of structural stress, begin refilling immediately:
Warning: Never attempt to push a lifted pool floor back down. The forces involved can cause catastrophic failure.
Before emptying your pool:
Call a pool professional immediately if:
The cost of professional consultation is minimal compared to potential structural repairs, which can easily reach $10,000-50,000 for severe hydrostatic pressure damage.
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