Draining a pool can be a necessary maintenance task, especially during repairs, renovations, or winterization. However, one of the most common questions pool owners ask is: Should I drain my pool below the return line? This decision isn’t as straightforward as it might seem and depends on several factors, including your pool type, weather conditions, and the reason for draining it.
In this comprehensive guide, we’ll explore everything you need to know about draining your pool below the return line, including what the return line is, the risks and benefits of lowering the water level, and professional best practices that can help protect your pool investment.
Understanding Pool Plumbing: What Is the Return Line?
Before deciding whether to drain your pool, it’s essential to understand the components involved in your pool’s plumbing system.
Components of Pool Plumbing
The return line is part of the pool’s circulation and filtration system. Water from the pool is drawn through the skimmer and pump, passes through the filter and heater (if applicable), and is then returned to the pool through the return jets—also known as the return line outlets.
Location of the Return Line
In most inground pools, the return line inlets (where water is pumped back into the pool) are positioned a few inches below the normal water level. Above-ground pools may have their return fittings closer to the top.
Why Water Level Matters Near the Return Line
Keeping the water level at least halfway up the skimmer opening is standard to ensure proper pump priming and avoid air intake. When considering draining below the return line, you might be removing water from these outlets entirely, which can impact system efficiency or even cause damage if not done correctly.
Reasons to Drain Your Pool Below the Return Line
While standard pool operation requires water to remain at or near the midpoint of the skimmer and return lines, there are legitimate reasons for lowering the water level below these points.
For Pool Maintenance
Certain maintenance tasks such as resurfacing, tile cleaning, or replacing underwater pool lights require lowering the water level significantly. For example:
- Refinishing the interior surface
- Replacing the skimmer or return fittings
- Conducting structural inspections below the waterline
Repairs Below the Return Line
If there is a structural crack in the pool wall, a malfunctioning return jet, or plumbing repairs needed below the standard water line, draining the pool may be necessary to access the problem area and perform a safe repair.
Winterization in Cold Climates
In colder regions where freezing temperatures can damage pool components, pool experts often recommend draining water below the return line to prevent freeze damage. This is usually part of a comprehensive winterization plan that includes blowing out lines and adding pool antifreeze.
Typical Steps in Winterizing a Pool Below Return Lines
- Balance water chemistry and clean the pool.
- Drain water to just below the return line (usually 18–24 inches below the skimmer).
- Blow out skimmer and return lines using an air compressor.
- Install winterizing plugs and cover the pool.
Key Risks of Draining Your Pool Below the Return Line
Even though there are valid reasons to drain your pool below the return line, the potential downsides should not be overlooked. Improper draining can lead to significant damage and expensive repairs.
Hydrostatic Pressure from Groundwater
For inground pools, groundwater can seep into the excavation area and exert upward pressure on the empty shell. This hydrostatic pressure can cause the pool to lift or “pop” out of the ground—a costly and catastrophic event.
When Hydrostatic Pressure Becomes a Threat
If you live in an area with a high water table or frequent rainfall, the risk increases significantly. Draining the pool without proper hydrostatic relief can be dangerous. Before draining, consult with your local pool professional or check if your pool has a hydrostatic valve that allows groundwater to enter the pool during heavy rain, equalizing pressure.
Structural Stress on Pool Components
Draining the pool places the structure under stress, especially if the water is removed too quickly. The empty shell loses the water’s weight, which normally stabilizes the pool. Without adequate support, the pool walls can bulge inward or even collapse.
Vinyl Liner Pools Are Especially Vulnerable
If you have a vinyl-lined pool and you drain the water below the return line, the liner can shrink, tear, or become misaligned, resulting in wrinkles and leaks. Once damaged, the liner may be unrepairable, requiring replacement.
Vacuum Sealing and Equipment Damage
When emptying the pool manually using a pump or siphon, care must be taken to avoid vacuum pressure building up in the pool’s plumbing system. Failing to open hydrostatic valves or air bleeds can cause seals and gaskets to fail in filters, pumps, and heaters.
Best Practices for Draining Your Pool Below the Return Line
If you have determined that draining your pool below the return line is necessary, such as for winterization or major repairs, follow these best practices to do it safely.
Check Local Codes and Pool Type
Before you begin, understanding the specific requirements for your locality and your pool type is essential:
| Pool Type | Drain Recommendation |
|---|---|
| Concrete (Gunite) | Usually requires water weight to resist pressure; draining must be done carefully |
| Steel/Fiberglass Inground | Less structural flexibility; drainage may not be recommended without support |
| Vinyl Liner Inground | High risk of liner shrinkage; draining often not advised |
| Above Ground | Can be fully drained for cleaning but not always necessary |
Hire a Pool Professional
In most cases, especially for inground pools, hiring a qualified pool technician is highly advisable. Professionals understand how to stabilize the structure, utilize hydrostatic relief, and manage sensitive plumbing lines safely.
Use the Right Equipment
Rent or use a high-capacity submersible pump to remove water efficiently. Avoid using smaller pumps that could require extended periods to drain the pool, which increases the risk of unexpected weather changes or groundwater pressure buildup.
Time It Right
Schedule pool drainage in dry seasons or when the water table is lowest. Avoid draining during rainy periods or under high humidity unless necessary. Never leave a pool unattended while draining.
Tips for Timing Your Drainage Process
- Drain during a dry, stable weather window.
- Complete the next steps (e.g., winterization or repairs) immediately after draining.
- Monitor local water tables if your area is prone to groundwater rise.
Monitor and Mitigate Risks
Check the water table by looking at nearby wells or using test holes. If groundwater is expected to rise, a hydrostatic valve can help relieve pressure and prevent damage. Additionally, you may need to install an internal support system, especially for vinyl or fiberglass pools.
When Draining Below the Return Line Is Safe vs. When It’s Not
Draining a pool below the return line depends heavily on the situation. Let’s compare specific scenarios when doing so is appropriate and when it’s best avoided.
Safe to Drain
| Scenario | Why It’s Safe |
|---|---|
| Winterization in cold regions | Standard pool maintenance required to prevent freeze damage |
| Internal repairs below the waterline | Access is crucial, and the project is time-sensitive |
| Skimmer or return jet replacement | Proper technique and tools are used for safe access |
Best to Avoid Draining
| Scenario | Why Draining Is Risky |
|---|---|
| High groundwater levels | Risk of pool flotation or hydrostatic pressure damage |
| Unsupervised or untested environment | Unexpected water table rises can cause immediate damage |
| Vinyl liner pool repair without liner removal | Liner shrinkage or wrinkling possible if pool is emptied improperly |
Alternatives to Draining Below the Return Line
If you’re not sure about fully draining the pool, several alternatives can help you get the job done without exposing your pool to unnecessary risks.
Spot Draining
Spot draining, also known as localized draining, involves lowering the water level just enough to fix a specific area. This method requires the use of a submersible pump placed strategically near the area needing repair.
Advantages of Spot Draining
- Lowers water minimally, protecting the pool structure
- Prevents hydrostatic pressure issues
- Can be done by pool owners with proper tools
Use of Waterproof Sealants and Covers
For smaller repairs like cracks above the normal water line, waterproof sealants and temporary water barriers may be used without draining the pool completely or even below the return line.
Professional In-Water Repairs
Skilled pool technicians can sometimes patch, seal, or replace parts of the pool while underwater. This technique avoids any need for draining and is usually very effective for small issues near the return lines.
Maintenance Tips for After Draining Below the Return Line
Once you’ve drained your pool below the return line, proper care is essential to return it to full functionality and avoid long-term issues.
Refilling the Pool Safely
If you live in a hard water area, refill the pool gradually to prevent plaster discoloration and damage. Fill to the midway point on the skimmer and continue adjusting as needed.
Check for Structural Integrity
After filling, inspect for new cracks, bulges, or movement that might indicate damage occurred during the emptying phase. A professional inspection may be necessary if you suspect any structural compromise.
Rebalance Water Chemistry
Refilling exposes the pool to new water, which will affect chemical balance. Test and adjust pH, alkalinity, calcium hardness, and chlorine levels afterward to protect both the water quality and your equipment.
Conclusion
So, should you drain your pool below the return line? The answer is it depends on your specific situation. For short-term repairs or necessary winterization, following safety protocols and industry standards makes it a viable and effective process. However, improper draining—especially in areas with high groundwater—can cause expensive and irreversible damage to the structure, lining, or plumbing.
Always consult a professional before draining your pool for any reason. Their expertise can help you determine the safest and most effective method based on your pool type, local climate, and the work needing to be done.
With the right planning, tools, and knowledge, draining below the return line can be a successful part of pool maintenance rather than a risk. Stay informed, take precautions, and keep your pool in top shape year-round.
If you’re unsure, err on the side of caution and preserve the water level unless a trained technician advises otherwise. After all, the primary goal is to extend the life of your pool—not compromise it.
Can draining my pool below the return line cause damage?
Draining a swimming pool below the return line can pose significant risks, particularly in areas with high groundwater levels. When the water inside the pool is removed, the external water pressure can cause the pool to lift or “pop” out of the ground, leading to structural damage such as cracks in the shell or shifting of the foundation. This is a common issue with in-ground pools and can result in costly repairs that may require professional intervention.
Additionally, even if groundwater isn’t a concern, draining below the return line can damage pool equipment and plumbing. Return lines are designed to expel water back into the pool, and operating the pump without proper water levels can lead to overheating or loss of prime. It’s essential to consult with a pool professional before deciding to drain the pool, especially if you’re uncertain about local water table conditions or the structural integrity of your pool.
Why would someone drain a pool below the return line?
There are a few specific scenarios in which draining a pool below the return line may be necessary. One common reason is for major repairs or resurfacing, where the entire structure must be emptied to properly address issues with the pool shell or plumbing. In some cases, draining below the return line may be required to replace or repair the return jets themselves or to perform extensive maintenance on the filtration system.
Another reason could be in preparation for winterization, particularly in colder climates where the water in the return lines needs to be fully evacuated to prevent freezing and subsequent damage. However, it’s important to note that these situations are exceptions rather than standard maintenance practices. Proper procedures and professional guidance should always be followed to avoid unintentional damage to the pool or its systems.
What are the main risks of draining a pool too low?
Draining a pool below the return line introduces several risks, particularly those related to structural integrity and equipment damage. Structural risks include hydrostatic pressure from groundwater pushing the pool upward, which can lead to serious damage such as cracking or shifting. This is especially common in areas with a high water table or after heavy rainstorms, when soil becomes saturated and increases pressure around the pool walls.
On the equipment side, draining the pool too low can cause the pool pump to run dry, leading to overheating and failure of the pump’s seals. It can also cause issues with the filtration system and heater, which rely on proper water levels for safe operation. These risks highlight the importance of understanding local conditions and having professional guidance when considering draining the pool beyond standard levels.
How can I safely drain my pool if needed?
If draining your pool is necessary—such as for repairs or winterization—it’s important to follow a safe process to prevent damage. Begin by contacting a professional pool contractor to assess your local conditions, including the groundwater level. They may recommend installing a hydrostatic valve or monitoring local water levels during the draining process. Use a submersible pump rather than the pool’s filter pump to empty the water safely and efficiently.
Additionally, make sure all pool equipment is turned off and disconnected before starting the draining process. Ensure pool covers, skimmer baskets, and any access panels are removed to relieve pressure and allow for an even drain. Never leave the pool unattended while draining and be prepared to stop the process if unexpected issues arise. Always consider environmental factors such as heavy rainfall that could impact groundwater levels and increase the risk of damage.
Are there alternatives to draining the entire pool?
In many cases, it’s not necessary to drain a pool below the return line to perform maintenance or address water quality issues. For example, tasks like routine cleaning, chemical balancing, or minor tile repairs can be done without fully draining the pool. If the water is discolored or contains high levels of solids, using flocculants and intensive filtration can sometimes avoid the need to remove large volumes of water.
When more extensive work is required, alternatives such as partially draining the pool or using bypass lines to work on specific systems may be available. Pool professionals can help determine the minimum water level needed to perform tasks efficiently and safely. These options not only reduce the risk of structural and equipment damage but also save water and lower the environmental footprint of pool maintenance.
What is the best time of year to drain a pool below the return line?
If it becomes necessary to drain a pool below the return line, the best time to do so is typically during the warmer months when groundwater levels are lower, and the risk of hydrostatic pressure is reduced. Avoid draining during or after heavy rainstorms when the surrounding soil may be saturated, as this increases the potential for the pool to float or sustain damage. Spring or early summer often provides favorable conditions with more predictable weather.
However, timing alone cannot fully eliminate the risk. It’s crucial to consult with local professionals familiar with groundwater trends in your specific area. Additionally, if your area experiences high seasonal water tables, it may be safest to keep the water level above the return line at all times unless repairs make it absolutely necessary to drain further. Strategic timing combined with expert guidance provides the best approach for pool draining safety.
How do I know if I should drain my pool below the return line?
Determining whether you should drain your pool below the return line depends on the specific situation you’re facing. Major repairs to the pool structure, such as resurfacing, replacing the main drains, or fixing cracks in the shell, may require a full or deep drain. Similarly, certain winterization procedures in cold climates might require lowering the water beyond the return line to protect plumbing from freezing.
However, many routine maintenance tasks—including cleaning, tile work, filter changes, and chemical adjustments—do not require such an extensive drain. Before making the decision, consult with a licensed pool technician or contractor who can assess your pool’s design, plumbing configuration, and environmental conditions. Their professional opinion will help determine whether this action is necessary or if alternative methods can achieve the same goals without introducing costly or hazardous risks.