When Should I Drain My Swimming Pool?

Written by Michael Dean
November 29, 2023

draining a swimming pool

Draining a pool is a big task that not only takes a while but will also cost you a lot in water bills when you eventually refill the pool. Luckily, this task doesn’t have to be done often. In fact, I recommend avoiding draining your pool if you can! But some issues are unavoidable, so in this article, I will break down some scenarios when you need to drain your pool and describe the best way to do it safely.

Main Takeaways

  • You should avoid completely draining your pool if you can, as it can lead to expensive repairs.
  • If you have to drain the water for water quality reasons, you typically only have to partially drain the water.
  • Always check your groundwater levels prior to draining your pool to avoid expensive damage to your pool’s structure.
  • Consult a professional if you are not comfortable. It is always cheaper to pay an expert than repair costly damages because you were unprepared.

Why You Shouldn’t Drain Your Pool

Completely draining your pool is a huge risk. This is NOT something you should do often, as it can cause major, irreversible damage to your pool. If done right, your pool can be practically unscathed, but an improperly drained pool can be catastrophic. Here are a few of the main risks involved with draining your pool.

The Pool Can “Float” or Heave Out of the Ground

This is one of the most dramatic issues that can occur when you drain your pool. When your pool is filled with water, there is equal pressure from the water in the pool and the ground on the outside of the structure. Draining the pool causes a sudden change, and the only hydrostatic pressure is coming from the outside of the pool. This can cause the pool structure to separate from the ground. If you have a fiberglass pool, this hydrostatic pressure change can cause the shell to crack.

Sun Exposure Can Damage your Pool

Empty pools are also susceptible to damage from sun exposure. UV rays can cause fiberglass pools to fade and break down vinyl liners, causing them to shrink.

Damage to Your Pump System

If you do not correctly adjust your filter, pool pipes, and waste lines, you risk damaging or burning out your pool’s motor. This can happen if the gallons per minute (GPM) of your pump exceeds the ability of your waste line to handle it. It can also occur if the filter sucks in air and runs dry. If that happens and you need to replace the unit, read my research on top-rated pool filters and top pool pump brands for specific recommendations.

Legal Issues

Did you know that, in some cases, you need a permit to drain your pool? So, you’ll need to do your research before draining, or you may earn yourself some hefty fees! Most municipalities do not allow you to dump pool water just anywhere. The approved location is usually your sewer system. However, putting too much water into your sewer system all at once can result in it backing up into your home.

Reasons Why You Would Have to Drain Your Pool as a Last Resort

As you can see, draining a pool is not a pool task that should be taken lightly. But there are a few situations in which it might be necessary to drain your pool completely. Here are some of the top reasons to drain and refill your pool. 

High Total Dissolved Solids (TDS) Levels

The most common reason that pool owners drain their pools is due to high levels of total dissolved solids (TDS). Total dissolved solids (TDS) accumulate in the pool water over time. Eventually, they cause water chemistry to become very unstable. This means more and more chemicals are required to maintain your pool water within the correct parameters. In some cases, if the TDS levels are WAY too high, you’ll need to drain your pool and refill.

High Levels of CYA or Calcium Hardness

Another reason you may consider draining your pool is when certain chemical levels are out of whack. That said, you will not need to completely drain your swimming pool for this. If your calcium hardness or cyanuric acid levels are extremely high, your best bet may be to partially drain and refill the water.

Acid Washing

If you have a concrete pool, you should drain and acid wash your swimming pool every 5 to 7 years if there is a lot of staining and buildup on the pool surfaces. There are obviously many ways to clean and maintain your pool without using something as extreme as acid, but sometimes, it is what your pool needs. Make sure to take the necessary safety precautions and wear PPE if you plan to acid wash a pool yourself.

Refinishing the Pool

The final reason why you may need to drain your pool is to resurface, replaster, or refinish it. Pool plaster, tiles, and other finishes can last decades if properly maintained, but there comes a time when you’ll need to refinish your pool. The first step in resurfacing a concrete pool is always draining. As I said, this won’t need to be done often, but it is an important part of caring for a concrete pool.

What Time of Year Is Best to Drain a Pool?

The best time of year to drain a pool is usually in the spring or fall when the weather is mild. If the temperature is over 85 degrees at any point in the process, it is best to postpone. The same is true of temperatures near or below freezing.

For this reason, I usually recommend spring as the best time of year to drain a pool because the water will be ready for some fresh summer swimming. Fall can work, too, but I do not recommend letting your pool remain empty over the winter, so you will need to at least partially refill it.

How to Drain Your Pool

So, despite the reasons not to drain your inground pool, you’ve determined that it’s necessary in your case. Well, I’m here to help you avoid those costly issues that may arise from incorrectly draining your pool.

Step One: Assess the Groundwater and Type of Pool

First of all, check the groundwater levels. If water levels in the area are high enough, they can cause your empty pool to pop out of the ground!

In addition, the type of material your pool is made of will make a difference. Specifically, fiberglass and vinyl liner pools require special treatment because they are typically not built to be drained completely. So, completely removing the water from these pools can cause bowing or cracking of the surface.

Step Two: Use a Sump Pump

Once you have assessed the groundwater situation and the needs of the type of pool you have, the safest way to drain your pool is to use a submersible pump, also called a sump pump. You can rent these from pool supply companies or hardware stores. While the filter pump can be used to drain a pool, you risk damaging an expensive piece of your pool hardware.

Step Three: Drain Properly

You should know where to drain the pool water. Often, pool owners will drain the pool into the sewer outlet of their property, but double-check this with your local authorities.

Note that sewer lines are not built to deal with huge quantities of water all at once, so the outflow should be kept to approximately 12 gallons per minute or less.

Step Four: Release the Pressure

Once the water level is low enough, grab a hammer and screwdriver to open the plaster covering the hydrostatic plugs. Then, unscrew the plugs to allow the groundwater to enter the pool. While this may seem counterintuitive, this important step keeps your pool from popping up!

When to Consult a Professional

If you are not 100% certain that your pool needs to be drained, you should consult a professional. Many pool repairs can be done underwater, and many problems with the water can be treated rather than drained entirely. If you do not know what the water table is in your area or are not entirely sure you know how to drain your pool, talk with a pool pro who can help. Note that you may also need a permit to drain your pool.

When you need to fill your pool back up, head to my article on pool water delivery and other options.

Frequently Asked Questions

Should I drain my pool to get rid of algae?

Not necessarily – draining your pool should be an absolute last resort. If you are dealing with an algae infestation, you should first try to tackle it by testing and adjusting the pH, shocking the pool, and filtering the water. Add some algaecide for good measure as well. These steps should help clear your green pool without having to go through the drastic measure of draining your pool entirely!

Why should pools not be drained?

Draining your pool can be an expensive mistake. If you do not drain your pool correctly, it could lead to extensive issues, such as the entire pool popping out! The costly repair bills can extend to the plumbing and deck as well.

How long does it take to drain a pool?

How long it takes to drain highly depends on the size of your pool and whether or not you use a sump pump. But generally, it’ll take anywhere between 8 and 16 hours to drain a pool.

Avoid Draining If You Can!

Draining your pool is risky business! In most cases, you can get away with not draining your pool. At most, pool owners will do a partial drain and refill. If you do find you have to drain your pool due to a needed acid wash or much-too-high TDS levels, make sure you do it correctly. Better yet, hire a professional to do the job for you. The last thing you want is to deal with some super-expensive repairs because your pool popped!

Do you have any more questions about draining a swimming pool or other pool-related queries? Let me know!

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