Every autumn, someone decides it is the perfect time to drain the pool: to clean it, re-tile it, repair a crack or simply "give it a rest". In a dry week, nothing happens. In a wet one, a concrete shell can try to do something no one planned for. It tries to float.
It sounds unlikely for a structure that weighs many tonnes. But it is a recognised failure in the pool industry, and winter is when the conditions line up.
Why an empty pool wants to rise
A pool full of water is heavy and is held down by that weight. Empty it, and the shell is far lighter, while any water in the ground around it still pushes up from below. If the water outside is higher than the water inside, the shell is under uplift.
AQUA Magazine, which covers the pool trade, published a piece on this by senior editor Eric Herman (March 2015). It quotes pool engineer Neil Anderson, who says the key factor is "differential head": the level of water outside the pool compared with the level inside. The volume of water around the pool is not the issue. For a fibreglass pool, a couple of inches of difference can be enough. For a gunite (concrete) pool he gives "as little as 18 inches", adding that this is "probably not as much as most people would think". The article also names two common misconceptions: that a concrete pool is too heavy to move, and that a relief valve cures the problem.
A civil and forensic engineer, Ron Koerth of Envista Forensics, makes the same point in a 2019 article: if there is not enough water in the pool and more water around it, the pool can "pop". For a concrete pool, he says, the result can mean demolition and rebuilding.
Both sources are North American, and neither mentions Cyprus. The physics, though, does not change at the border.
Why winter in North Cyprus is the risky season
According to the Climate of Cyprus entry on Wikipedia, the island averages around 500 mm of rain a year, falling mainly between November and March, with December to February accounting for about 60% of the annual total. The northern coastal plains average 400 to 450 mm. In other words, a large share of the year's rain arrives in a few months, often in heavy spells.
We have not found published groundwater data for Kyrenia, Alsancak, Lapta or Esentepe, so we cannot tell you how high the water table sits on your plot. That varies with the slope, the soil and the drainage, and a pool on a hillside site can face runoff as well as groundwater. The AQUA article lists draining for winterising, repair or replacement while outside water rises from a storm, snowmelt or seawater intrusion as the classic trigger. It describes concrete pools "down two or three feet over the winter" that popped after spring rain.
The relief valve is insurance, not a guarantee
Many concrete pools have a hydrostatic relief valve at the deepest point. If the pressure outside is higher than inside, it lets groundwater into the pool so the levels equalise. AQUA's source calls it an "inexpensive insurance policy".
But it is not a cure-all. Valves can fail to open, or relieve pressure too slowly. Koerth notes they are known to get jammed with dirt and debris. AQUA reports a pool lifted by a jammed valve to a 45-degree angle that had to be replaced rather than reset.
So the questions for any villa owner are simple. Does your pool have a valve? Where is it? When was it last checked? On a villa you bought second-hand, the answers may not be written down anywhere.
A practical winter checklist
- Leave the pool full unless there is a reason to empty it. AQUA is clear that the danger point is when a pool is drained for maintenance or the level drops during winterisation. A Mallorca real-estate guide to pool winterising (FALC, undated) also advises that an outdoor pool usually goes through winter with water in it.
- If you must drain it, have it assessed first. Ask a builder to check ground conditions and the relief valve before a single litre goes out. A sump beside the pool lets you see the external water level and, if needed, lower it with a pump. If you have none, that is worth knowing.
- Choose a dry spell, and don't leave it empty. Repair and refill promptly. A pool left empty for weeks through a wet month is the scenario the pool trade warns about.
- Keep surface water away from the pool. Anderson's main advice is good drainage around the outside, so water outside is never higher than inside. Check gutters, terrace falls and any drain that discharges near the pool.
- Fix a falling water level before winter. If your pool loses water faster than evaporation explains, find out why now, rather than discovering it with a low pool and a wet forecast.
- Cover it and keep it clean. Frost is rare on the Kyrenia coast, so the freezing advice in northern-European guides mostly doesn't apply, but storm debris and leaves do.
- Look at the surround. Cracks opening in the paving or coping, or a gap forming between the pool edge and the surround, deserve a proper look. This is our practical observation rather than a statistic, but movement is easier and cheaper to deal with early.
Planning an empty-pool repair properly
When tiles, waterproofing or the shell itself need work, the pool does have to be emptied. A well-run job starts with the ground, not the pump. Ask your contractor:
- What is the groundwater situation on my plot, and how do you know?
- Is there a relief valve, and is it working?
- How will the pool be drained, how fast, and what is the plan if it rains?
- How long will it stay empty, and what is the refill plan?
- Can the scope and sequence be written down before work starts?
If the answers are vague, that is information too.
How 365 Build & Design can help
We would rather look at your pool before you drain it than repair the consequences afterwards. We build swimming pools, tile pool surrounds, and handle landscaping, plumbing and waterproofing, and we can assess a pool and its surroundings and tell you plainly whether it can be emptied safely. If something is outside what we undertake, we will say so.
365 Build & Design is NHBC certified and an officially registered TRNC company based in Kyrenia, with a fully English-speaking team and a 5-star Google rating. We work across Kyrenia, Alsancak, Lapta, Esentepe, Famagusta, İskele and Nicosia.
Talk to 365 Build & Design about your project.
WhatsApp: https://wa.me/905428833240 Website: https://365builddesign.com/
Sources
- AQUA Magazine, Eric Herman, "Pressure Points" (11 March 2015): https://www.aquamagazine.com/home/article/15119622/pressure-points
- Envista Forensics, Ron Koerth, "Floating Swimming Pools: Part II" (16 May 2019): https://www.envistaforensics.com/blog/floating-swimming-pools-part-ii
- Wikipedia, "Climate of Cyprus": https://en.wikipedia.org/wiki/Climate_of_Cyprus
- FALC Real Estate, "How to Winterize Your Pool" (undated): https://falcrealestate.com/en/magazine/winterise-the-pool
