Leaving a fibreglass pool empty might seem like a harmless decision, but it can cause serious problems that often cost far more than expected to repair. The water inside your pool isn’t just there for swimming – it provides vital support to the fibreglass shell, keeping it stable against soil and groundwater pressure. Without it, your pool is left vulnerable to structural issues, movement, or even lifting out of the ground. If you’ve ever wondered whether draining a pool is safe, here’s what really happens and what you should consider before taking that step.
Risks Of Leaving A Fibreglass Pool Empty
When you take the water out of your pool, the shell no longer has the counterbalance that normally keeps it in place. Soil around the pool is constantly shifting due to rain, groundwater levels, and even temperature changes. The water inside the shell acts like a stabiliser, pressing back against those forces. Without it, the ground pressure can cause the pool walls to bow or crack.
In some cases, hydrostatic pressure builds up underneath the pool shell. If this pressure is stronger than the weight of the empty shell, the pool can literally lift or “pop” out of the ground. This isn’t just rare or unusual – it’s a very real risk, especially in Perth where clay and sandy soils behave differently depending on weather. Even if you don’t see damage immediately, the stress can create hairline fractures in the fibreglass that worsen over time. Repairing this kind of damage can be both complicated and costly.
Why Water Supports The Shell
Fibreglass pools are engineered to hold water. The weight of the water balances the surrounding soil and prevents uneven pressure from building up. Think of it as the pool and the ground working together – the shell is built to stay strong when filled, not when empty.
When you remove the water, the shell is exposed to external forces it was never designed to handle. This can lead to distortion, bulging, or separation from the surrounding structure. Even seasonal changes, such as hot summer days followed by cool nights, can cause the fibreglass to expand and contract more dramatically when there’s no water inside to regulate the temperature. Over time, these stresses can weaken the shell and shorten the lifespan of your pool. By keeping water in place, you’re protecting the long-term stability of your investment and avoiding unnecessary damage.
Situations Where Draining Might Be Necessary
Although draining your pool comes with risks, there are times when it may be unavoidable. For example, major repairs, resurfacing, or addressing a severe chemical imbalance may require the pool to be emptied. But draining should always be considered a last resort.
If you do find yourself in a situation where draining is the only option, professional guidance is essential. Experienced pool specialists know how to safely manage the risks by checking groundwater levels, using pumps correctly, and monitoring pressure around the pool shell.
Attempting to do it yourself increases the chances of damage and often results in higher repair costs than simply engaging an expert in the first place. Every backyard environment is different, which means what works for one pool may not be safe for another.
Maintenance Alternatives To Draining
The good news is that most water quality issues can be fixed without draining your pool. Cloudy water, algae growth, or imbalanced chemicals can all be corrected with the right maintenance steps. By choosing safer methods, you avoid exposing your fibreglass shell to the dangers of being left empty.
Steps You Can Take Instead
Shocking the water
A chlorine shock treatment can quickly kill bacteria, restore clarity, and reset water balance. It’s one of the fastest ways to recover from algae outbreaks or cloudy conditions.
Balancing chemicals
Testing and adjusting pH, alkalinity, and calcium hardness ensures the water stays safe for swimmers and helps protect your pool surface. Even small imbalances can be corrected without draining.
Improving circulation
Running your pump and filter for longer cycles improves water flow, prevents stagnation, and helps remove particles that cause cloudiness. Sometimes, all your pool needs is better circulation to bounce back.
Partial water replacement
If chemical levels are too high, replacing a small percentage of the water at a time is often enough. This method reduces build-up without exposing the shell to the risks of a complete drain.
By using these alternatives, you can restore water quality, maintain a healthy swimming environment, and extend the life of your pool – all without putting your fibreglass shell at risk.
What To Do If You Must Drain Your Pool
If draining your pool is absolutely unavoidable, planning and preparation are critical. Choose a period of dry weather, when groundwater levels are lower, to reduce the pressure under and around the pool. Before beginning, speak with a qualified professional who can assess the site conditions and take the necessary precautions.
Professionals may use hydrostatic valves, sump pumps, and monitoring systems to manage groundwater pressure during the process. These precautions help reduce the risk of the shell lifting or shifting. Attempting to drain the pool without this knowledge and equipment can lead to irreversible damage that costs far more than professional care.
By seeking expert advice, you safeguard your pool and ensure the work is carried out with minimal risk. Remember, your fibreglass pool is a long-term investment, and protecting it during maintenance is far more cost-effective than repairing damage caused by rushing into a DIY drain.
