At various points in their lifespan (usually every 5 years), swimming pools need to be pumped and drained.
This could be necessary to swap out water that can no longer stay sanitary, acid wash the interior walls, perform repairs or resurfacing on the pool on the pool, or all three.
But the answer to the question of how long can you leave a pool empty is this: not very long at all.
Here’s why…
The Problem With An Empty Pool
Pools are designed to hold water. When there’s no water in them, they’re at risk of damage as there’s nothing keeping them weighed down.
To give you some perspective, a modest sized 10,000 gallon pool weighs over 83,000 lbs. When that amount of weight and pressure is removed from the structure, the pool can actually pop out of the ground due to ground pressure forcing it up.
This can compromise its structural integrity, damaging the walls, floor, liners, and even the deck itself. Newer pools equipped with hydrostatic relief valves on the pool floor will help to keep the shell in place, lessening the chance of popping.
Additionally, a lack of water means there’s a lack of moisture on the pool walls. If left exposed to long periods under the hot sun, pool finishes will dry out, creating cracks and flaking.
How Long Can An Inground Pool Stay Empty?
Pools are crafted from various materials that can affect how the structure acts when it’s drained of water.
As you might expect, there are also some nuances to be aware of depending on whether you have a concrete, fiberglass or vinyl liner pool.
Concrete Pools
There’s a misconception that due to the weight of concrete, these pools have less of a tendency to pop out of the ground. That would be incorrect, as concrete pools are just as at risk at any other inground pool.
When a pool is full, hydrostatic pressure pushes against the walls and floor from the inside while groundwater pushes against the structure’s exterior and underside. Once water is removed (and subsequently, the interior hydrostatic pressure), if there’s an influx of groundwater, it will push the pool up and out of place.
As a general rule, you shouldn’t keep any pool empty for longer than it needs to be. Get the work done that you needed to do and refill it as soon as possible.
Vinyl Liner Pools
Vinyl liner pools use braced steel, aluminium, or plastic panels as their perimeter shell and have a vinyl liner installed over the walls and floor. This makes them a more lightweight structure than a concrete pool.
There’s great debate as to whether or not you should ever drain a vinyl liner pool, but the reality is, at some point, the liner will need to be replaced.
But again, like other types of pools, if the pool is drained then the structure can shift and become damaged.
Additionally, because the vinyl liner is vacuum sealed to the structure and held in place by water pressure, draining it can cause the liner to bubble when you refill it. Sunlight can also cause the liner color to fade when water isn’t present in the pool.
Fiberglass Pools
Fiberglass pools are a lightweight shell that are extremely prone to popping out of the ground during a drain.
To help combat this, some models are anchored in place during the backfill process. This allows the exterior shell to grip the earth in a bid to keep it stable during a drain.
Additionally, a cantilevered edge around the perimeter of the pool is designed to hold it in place when the pool is without water.
As usual though, if your backyard is prone to large amounts of groundwater, you need to be extra careful about how much water you remove from the pool.
What About Above Ground Pools?
While above ground pools won’t pop out of the ground, the issue they can present during a drain is the shrinking of their pool liner due to changes in pressure, and exposure to air.
This is common with older vinyl liners, resulting in tears occuring during the refill process.
The weather will also play a role, as cold days constrict the liner and make it less malleable, which may result in damage.
Think Twice About Draining
Not only are pool drains time consuming, but they’re also expensive. Add in the potential damage that can occur when the pool is empty, and there’s a strong case to be made for doing a drain only if it’s absolutely necessary.
Many problems that people drain their pools for can actually be fixed while the swimming pool is still full of water.
There may be a situation where the pool water goes haywire and requires dilution to bring it back into balance, but you’ll only have to partially drain it to dilute it.
Likewise, acid washing the pool walls and floor can be done by letting the pH level become acidic to the point where the water will eat away at the grime and stains.
It’s really only when major repairs, resurfacing, or replacing of a liner are needed that you should consider draining your pool.
No Diving!
How long can you leave a pool empty? Well, the minimum amount of time possible in order to minimize the risk of serious damage.
Most issues that require a pool drain will take at least a day or two to resolve, but it’s recommended to not let it sit empty for any extended period of time.
