If you’re a new pool owner or you’re considering installing a pool, one topic worth understanding is when a swimming pool may need to be partially or completely drained. Fortunately, completely draining a pool isn’t something most homeowners should need to do very often. In fact, there are good reasons to avoid it unless it’s actually necessary.
An inground swimming pool isn’t simply a big container that can always be emptied and refilled without consequence. Removing thousands of gallons of water changes the forces acting on the pool structure. Depending on the type of pool, groundwater conditions and other factors, improperly draining an inground pool can damage the surface, liner or shell and, in extreme circumstances, allow hydrostatic pressure to push the pool upward.
There’s also the question of where all that water is going. Local regulations may restrict how or where swimming pool water can be discharged, particularly when it contains chlorine, salt or other pool chemicals.
For those reasons, don’t completely drain an inground pool simply because the water has become difficult to manage. First determine why water replacement is necessary and whether a partial drain and refill can accomplish the same thing. If a complete drain is required and you’re uncertain about the risks or proper procedure for your particular pool, this is a job worth discussing with an experienced pool professional.
When Might You Need to Drain a Swimming Pool?
There isn’t one universal schedule for draining a residential swimming pool. Many pools can go for long periods without being completely emptied, while partial water replacement may occasionally be useful for managing water chemistry.
There are also certain repairs and renovations that may require much more of the water to be removed. Here are several situations in which partial or complete draining might be considered.
1. When a Water Problem Can’t Be Corrected Normally
An algae outbreak doesn’t automatically mean you need to drain the pool. Most algae problems can be addressed by correcting water chemistry, maintaining adequate sanitizer, brushing affected surfaces and making sure the filtration and circulation systems are operating properly.
If you’re repeatedly fighting algae or other water-quality problems, try to determine the underlying cause before assuming that replacing all the water will solve it. A persistent problem could involve water chemistry, filtration, circulation, contamination or another issue that will still exist after the pool is refilled.
There may be unusual circumstances in which water replacement becomes part of the solution, but a complete drain generally shouldn’t be your first response to green water or an algae outbreak.
2. For Certain Repairs or Renovations
Some major pool repairs and renovations require the water level to be lowered significantly or the pool to be completely drained. Resurfacing a concrete pool is an obvious example. Certain structural repairs, surface work and other renovations may also require an empty pool.
Vinyl-liner work requires particular care. Water helps hold a vinyl liner in position, and completely draining a vinyl-liner pool can allow the liner to shift, shrink or otherwise become difficult to reinstall properly. Liner replacement is therefore a good example of a project where you should follow the pool or liner manufacturer’s procedures and consider having the work handled by an experienced professional rather than simply pumping the pool dry yourself.
Fiberglass pools also require special consideration because groundwater pressure outside the shell can create serious problems when the weight of the pool water is removed.
The bottom line is simple: if a repair requires completely emptying an inground pool, make sure you understand the requirements and risks for that particular type of pool before removing the water.
3. For Certain Types of Surface Work
Routine pool cleaning shouldn’t require draining the pool. Brushing, vacuuming and normal surface maintenance are generally performed with the water in place.
More extensive surface restoration can be different. Depending on the pool finish and the work being performed, resurfacing, stain treatment or repairs may require lowering the water level or completely draining the pool.
Don’t drain half the pool simply because a stain or dirty surface is difficult to clean. First identify the problem and determine the appropriate treatment for your particular pool surface. If draining is necessary, remove only as much water as the procedure actually requires and follow the recommendations for the pool and surface material.
4. When Water Chemistry Calls for Partial Replacement
Sometimes the reason for replacing pool water isn’t something you can see. Over time, dissolved materials can accumulate in swimming pool water as chemicals are added and water evaporates and is replaced.
One measurement used to track this is Total Dissolved Solids, usually abbreviated as TDS. Instead of assuming that every freshwater pool should remain below a fixed TDS number, it is more useful to compare the pool’s current TDS with its baseline level when the water was fresh and properly balanced.
A commonly used industry guideline considers TDS a concern when it reaches approximately 1,500 parts per million above that starting level. Saltwater pools require a different baseline because the salt intentionally added for the chlorine generator substantially increases the TDS reading from the beginning.
High TDS isn’t automatically a reason to empty an entire pool. Partial water replacement is commonly used to reduce it, and other water-chemistry conditions may also be managed by replacing only a portion of the pool water.
If you’re having persistent problems with water balance, cloudiness, scaling, corrosion or other water-quality issues, test the relevant chemistry rather than relying on appearance alone. Water replacement may be part of the solution, but knowing what you’re trying to correct will help determine how much water actually needs to be replaced.
Think Before You Pull the Plug
There are legitimate reasons to partially or completely drain a swimming pool, but doing so shouldn’t be treated as ordinary routine maintenance. An empty inground pool can be vulnerable to groundwater and hydrostatic pressure, and different pool structures respond differently when the weight of the water is removed.
Weather matters too. Groundwater can be particularly concerning after periods of heavy rain or in areas with a naturally high water table. If you don’t know the groundwater conditions around your pool or how its hydrostatic-pressure protection works, get professional guidance before completely draining it.
You’ll also need a safe and legal place for the discharged water to go. Check applicable local requirements rather than simply sending thousands of gallons across the lawn, into the street or toward a storm drain.
When water replacement is needed, a partial drain and refill may sometimes accomplish the goal without exposing the pool to all of the risks associated with completely emptying it.
In the next article in this series, we’ll take a closer look at methods and practical considerations for draining different types of swimming pools.
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