As summer draws to an end and the weather starts getting colder and colder, many pool owners start thinking about how they are going to handle the upcoming winter. Should they bother going through the hassle of properly winterizing their pool, or should they just drain their pool so that they don’t have to deal with it?
Unfortunately, many new pool owners learn the hard way that draining their pool is a mistake that leads to expensive repairs or even permanent damage. In general, you should not drain your pool – whether it’s an inground or above-ground pool – unless absolutely necessary.
Above-ground pools are more acceptable to drain because some of them are not designed to be left out in the cold. The ones that can endure the cold should be left outside full of water. Inground pools, for the most part, should rarely ever be drained except under certain conditions.
In this article, I will go over the reasons why you should almost never drain your pool even during the winter, the risks of draining it, and when it is okay to drain a pool.
The risks of draining an above-ground pool for the winter
First, read the instruction manual that comes with your above-ground pool and see if it states whether it can be left out in the winter or not.
Temporary pools are not durable enough to withstand the freezing temperatures which can cause irreparable damage to the components. These pools must be drained, carefully dried, and stored in a temperature-controlled space for the winter to prevent damage and mold growth.
Above-ground pools that have a vinyl liner are typically the kinds of above-ground pools that can be left outdoors in the winter, and these ones should NOT be drained.
The vinyl liner is very delicate. If exposed to sunlight or left to dry, it will shrink, lose elasticity, and become stiff and brittle. Even if you add water back to it, the liner can easily crack like grass.
The only time you should drain an above-ground pool is if your intention is to replace the liner and you don’t care if the old one dries out. Even refilling the pool with water shortly after draining will not be enough to restore it to the condition it once had.
Lastly, some above-ground pools are designed such that they rely on the weight of the water to hold the frame in place and provide outwards pressure so that it can withstand any external forces caused by the elements.
The risks of draining an inground vinyl liner pool for the winter
Inground vinyl liner pools have a minimum safe water level that must be adhered to at all times (around 6-12 inches from the bottom of the shallow end).
Draining past this point can result in damage to your pool liner similar to what was described in the section above.
However unlike above-ground pools, which are flat-bottomed, inground pools tend to have a shallow and deep end. The liner is held in place by having water in it at all times.
As soon as there is no weight holding down the shallow end, the liner will start to get stretched in any place that is firmly held in place. However, since they are held firmly in place, the resulting stress is applied to the liner which stretches, distorts, weakens, and tears at the vinyl liner.
That is why you should generally not drain your inground vinyl pool past the shallow end, as it will get damaged otherwise.
Additionally, the walls of a vinyl lined pool are not particularly strong and are designed to hold up the weight of the surrounding earth only when it is filled with water. Leaving a vinyl lined inground pool empty puts it at risk of structural failure such as shifting or bowing of the walls, or a collapsing of them.
Should these things occur, you have to completely redo your pool installation and it will be costly.
The risks of draining a concrete pool for the winter
Concrete pools are the most durable type of pool but draining them for winter is still a bad idea. Unfortunately, enough people have managed to drain their pool and leave it empty for the winter so they claim that it is safe to do so. They should count themselves lucky.
There is certainly a survivor’s bias going on here, because the pool owners who do encounter issues encounter catastrophic issues.
First, much of the same issues that the other pool types face are also encountered in a concrete pool. Without a layer of water to protect it, even concrete will experience wear and tear when exposed to the elements, causing it to deteriorate much faster than normal.
The interior surface of a concrete pool is the single most expensive maintenance cost and all of them are designed to be used underwater. When left to dry, some will fail as they delaminate, crack, and generally become brittle.
The scariest, most disastrous issue is something called float. When a concrete pool is filled with water, it becomes heavy enough to be held firmly in the ground. When empty, as heavy as the concrete is, it can be pushed out of the ground given enough hydrostatic pressure underneath.
This can happen if, for example, the hydrostatic relief valve is blocked, or there are unusually heavy rains or flash food conditions. Basically, if there is a bunch of groundwater underneath the concrete pool, then like a boat on rising tides, it can literally float or pop out of the ground.
As you can imagine, the damage to the surroundings will be immense should the pool pop out. Furthermore, once a pool has popped out, then it cannot be put back in the ground.
Better to winterize your pool and leave the water in to protect it from these other risks, than drain it and risk it popping out of the ground.
The risks of draining a fiberglass pool for the winter
Like concrete pools, fiberglass pools are held firmly in place by the weight of the water inside. In fact, since the shell of a fiberglass pool is much lighter than concrete, it needs the extra weight much more than a concrete pool.
Furthermore, they are also not as durable as concrete* and need water to exert pressure against the walls to protect against bowing, shifting, twisting, collapsing, or any other force that might be applied to it.
*Actually, fiberglass pools are technically more durable than concrete assuming they are equally thick, but fiberglass pools are designed such that they are much thinner whereas concrete pools are up to a foot thick or more.
And if you were to drain the pool, it risks popping out like a concrete pool, but it also risks total collapse as well, much like a vinyl lined pool. Whatever the case, don’t drain your fiberglass pool.
When is it okay to drain a pool?
After reading all of the doom and gloom above, and also hearing pool experts explicitly use the word “never” as the answer to when you should drain your pool, it seems pretty clear-cut: never drain your pool. Ever.
Of course, the reality isn’t literally never, but rather the circumstances when you should drain your pool are so infrequent – and when they arise you probably need professional help with it anyway – that the average pool owner might as well never drain their pool.
What are these specific conditions when it is okay to drain the pool, you ask? I cover them below:
- For major repairs: Most repairs can be done in the water without draining the pool. Larger jobs like fixing large cracks or repairing the plumbing warrant draining the pool for.
- For deep cleaning: Once every 5 years or so, your pool needs to be thoroughly cleaned. Typically, a full acid wash is done and/or the pool surface is refinished.
- To lower TDS: When your Total Dissolved Solids (TDS) factor is too high, a partial draining and refilling of the pool may be warranted. Since there is still water left in the pool, most of the risks outlined in this article are avoided.
However, you should consider getting a professional opinion first. If a pool does need to be drained, you should let a professional handle it. They will use bracing equipment that can hold up the walls of an empty pool so that it doesn’t collapse and can do the cleaning or repairs for you.