Can a Gunite Pool Be Left Empty? What Every Pool Owner Needs to Know

Draining a pool might seem simple. Pull the plug, let it empty, handle the repairs, then refill. But when it comes to gunite pools, the decision is more complicated than it looks.

So, can a gunite pool be left empty?

Yes, but only briefly and under the right conditions.

A gunite pool is a solid concrete structure, but it relies on the weight of pool water to stay balanced against pressure from the surrounding ground. Leave an empty concrete pool sitting too long, and you increase the risk of hydrostatic pressure issues, cracking, and structural movement.

Before you drain the pool, it’s important to understand what’s happening beneath the surface and how to protect your investment.

Key Takeaways

• In many cases, a gunite pool should not stay empty for more than about two weeks, and in high-water-table areas even less may be advisable.

• Hydrostatic pressure from groundwater is the biggest threat.

• A high water table dramatically increases risk.

How a Gunite Pool Actually Works

A gunite pool is a type of concrete pool constructed by spraying a mixture of cement and sand over steel rebar. Once cured, it forms a dense, durable pool shell built directly into the ground.

But here’s what many homeowners don’t realize.

Your swimming pool is not just a concrete structure sitting in soil. It is a carefully engineered system designed to balance internal and external pressure.

The pool water inside pushes outward against the pool walls and downward against the pool floor. At the same time, groundwater pressure in the surrounding soil pushes inward and upward against the pool structure.

When the pool water is present, these forces balance each other.

When the pool sits empty, that balance disappears.

Why Pool Water Is Structurally Important

Water is heavy. Very heavy.

That weight inside your gunite pool counteracts groundwater pressure beneath and around the shell. When you remove that weight and leave an empty swimming pool exposed to the ground’s natural pressure, problems can develop.

Hydrostatic pressure builds beneath the concrete floor. Soil moisture and groundwater push upward. Over time, this imbalance can lead to structural damage.

The longer the pool's empty condition lasts, the greater the risk.

Why Homeowners Drain the Pool

There are legitimate reasons to drain the pool. In fact, some repairs simply cannot be done without the pool being drained completely.

Structural repairs. Cracks in the pool shell, plumbing repairs, or resurfacing projects often require draining your pool.

Acid wash or deep cleaning. An acid wash is sometimes necessary for severe staining or scale buildup. Deep cleaning projects may also require draining.

Major chemical imbalance. If pool chemicals become severely imbalanced or total dissolved solids rise too high, a water replacement may be necessary.

However, most pools do not need to be fully drained for routine maintenance. Many algae issues, cloudy water problems, or chemical corrections can be handled without fully draining.

Draining should never be routine.

How Long Can a Gunite Pool Stay Empty?

There is no universal hard rule, but in many cases, a gunite pool should not stay empty for more than about two weeks. In areas with a high water table or after heavy rain, even less time may be advisable.

Some builders and service professionals take a more conservative approach and recommend limiting an empty pool to just a few days to a week, depending on groundwater levels, soil conditions, and weather.

Others may be comfortable allowing a slightly longer dry period under very controlled conditions, such as during a dry season with low groundwater and active dewatering measures in place.

The key point is this: the longer the pool stays empty, the greater the structural risk. Once you move into an extended period without water, hydrostatic pressure and environmental exposure begin increasing the potential for cracking, shifting, or surface damage.

Draining should always be carefully planned and monitored, with a clear schedule to refill as soon as repairs or maintenance are complete.

The Real Risk: Hydrostatic Pressure

Hydrostatic pressure is the upward force created by groundwater beneath your pool.

A gunite pool is designed to balance internal and external forces. The weight of the pool water pushes outward against the pool walls and downward against the pool floor. At the same time, groundwater pressure pushes inward and upward from the surrounding soil.

When the water level drops or the pool is fully drained, that internal counterweight disappears. Groundwater pressure can then build beneath the pool shell.

In certain conditions, especially where groundwater levels are elevated, this pressure can cause cracking, shifting, or structural movement. In rare but documented cases, severe hydrostatic pressure has even lifted pools partially out of the ground.

While that outcome is uncommon, the underlying mechanics are real. The purpose of careful timing, proper drainage procedures, and hydrostatic relief systems is to minimize that risk and protect the pool’s integrity.

High Water Table and Heavy Rain Concerns

If it has rained recently, groundwater levels may already be elevated. Heavy rain increases water pressure in the soil. Draining your pool in these conditions adds unnecessary risk.

A high water table means groundwater sits closer to the surface. That increases hydrostatic pressure against the pool shell.

If you suspect high groundwater conditions, consult a pool professional before draining.

Structural Damage That Can Occur

When an empty pool is left too long, several structural issues can develop.

Cracking. Without water pressure inside, the concrete can shift slightly. Small cracks may form. Over time, those cracks can expand and lead to leaks.

Pool walls shifting. Soil pressure around the pool walls may cause subtle movement. Even minor shifting can compromise the pool’s integrity.

Hydrostatic uplift. This is the most severe scenario. Groundwater pressure lifts the pool structure from below. While gunite pools are durable, they are not immune to groundwater pressure.

Surface damage. When the pool drained condition lasts too long, exposed surfaces dry out.

Sunlight and heat can dry plaster and exposed finishes, increasing the risk of surface cracking. In colder climates, freeze thaw damage can occur if moisture within the concrete expands during freezing conditions.

The Role of the Hydrostatic Relief Valve

Most inground pools include a hydrostatic relief valve at the bottom of the pool.

This valve allows groundwater to enter the pool when internal pressure drops, helping equalize pressure beneath the shell and reduce hydrostatic pressure buildup.

However, this is not a guarantee of safety.

The hydrostatic relief system must be functioning properly, and even then, it is not a substitute for minimizing the amount of time the pool remains empty. It is simply one layer of protection.

Weather Matters More Than You Think

Timing plays a bigger role than most homeowners realize when draining a gunite pool. Even a well-built pool can face added stress if weather conditions are not ideal.

Avoid freezing weather. Freeze-thaw cycles are tough on exposed concrete. Moisture within the surface can expand as temperatures drop, increasing the risk of cracking along the pool floor or walls. Without water inside to help stabilize pressure, an empty pool is more vulnerable during cold weather.

Avoid heavy rain. Draining right after heavy rain raises the risk because groundwater levels are often higher. Increased groundwater pressure pushes upward against the pool shell, adding stress while the pool is empty.

Avoid extreme heat. Prolonged sun and high heat can dry out plaster and finishes. When a pool sits empty in hot conditions, surfaces may shrink slightly or develop minor surface damage that affects long-term durability.

If draining is necessary, choose mild, dry weather with stable temperatures to help protect the pool structure and surface.

Signs You Should Not Drain the Pool

In some situations, draining your swimming pool creates more risk than benefit. Before you drain the pool, evaluate the pool structure and surrounding conditions.

Avoid draining if you notice:

• High water table in your area. Groundwater sitting close to the surface increases pressure beneath an empty concrete pool and can lead to structural stress.

• Heavy rain recently. Saturated soil raises groundwater pressure against the pool shell.

• Visible cracks in the concrete pool. Existing structural issues can worsen once the stabilizing weight of pool water is removed.

• Known leaks in the pool shell. An empty pool can cause leaks to expand and lead to more serious repairs.

If any of these conditions apply, getting a second opinion from a pool professional is a smart step before draining your pool.

Safer Alternatives to Full Drainage

Before draining your pool, consider safer options. Many pool issues can be resolved without creating an empty pool.

Partial drain. Lowering the water level instead of fully emptying the pool can allow certain repairs or adjustments while reducing structural risk.

Deep cleaning without full drain. Many algae and water clarity problems can be corrected through proper maintenance and chemical treatment without draining the entire swimming pool.

Regular maintenance. Consistent maintenance, balanced pool chemicals, and routine inspections help prevent situations that require full drainage.

Draining should always be treated as a last resort.

Gunite vs Fiberglass vs Vinyl

Different types of inground pools respond differently when empty.

• Gunite pools. The heavy concrete shell provides strong structural stability, but the pool still relies on the weight of water to maintain balance.

• Fiberglass pools. Lighter shells make fiberglass pools more vulnerable to uplift from groundwater pressure when the pool stays empty.

• Vinyl liner pools. Vinyl liners can shrink, wrinkle, or shift if the pool is drained for an extended period.

Even with the strength of gunite, leaving a concrete pool empty too long can increase the risk of cracking, leaks, and structural movement. Properly draining your pool and refilling it promptly helps protect the pool’s integrity.

Expert Pool Care from Ferrari Pools: Custom Outdoor Living

At Ferrari Pools: Custom Outdoor Living, we design and build custom gunite pools engineered for long-term durability. Draining a concrete pool is sometimes necessary for repairs or resurfacing, but leaving a pool empty for too long can increase the risk of structural damage and costly repairs.

Our team understands how groundwater, soil pressure, and structural balance affect inground pools. With the right drainage and refill plan, you can help prevent damage to the concrete structure.

In addition to custom pool construction and renovations, we also provide hot tubs, swim spas, pool openings and closings, water testing, and chemical guidance through our retail store, and ongoing maintenance support.

If you are planning repairs or considering draining your pool, call Ferrari Pools: Custom Outdoor Living to discuss the safest approach and protect your investment for years to come.

Conclusion

So, can a gunite pool be left empty?

Yes. But only for a limited time and under the right conditions.

In many cases, keeping a gunite pool empty for more than about two weeks increases structural risk. In high water table conditions or after heavy rain, even less time may be advisable.

Hydrostatic pressure is real. Groundwater pressure can cause cracking, structural movement, and costly repairs if not properly managed.

Draining your pool should always be a carefully planned decision, not routine maintenance.

When handled correctly and refilled promptly, your gunite pool will remain strong, stable, and ready to enjoy for decades to come.

Frequently Asked Questions

What happens if you don't water gunite?

New gunite must stay moist during the curing process so the concrete can gain strength properly. If it dries too quickly, it can lead to surface cracking and reduced durability. After the pool is finished and filled, the curing process is complete and watering is no longer needed.

Is it okay to drain a gunite pool?

Yes, but only when necessary for repairs, resurfacing, or major water issues. A gunite pool should not remain empty for long because groundwater pressure can stress the structure. When draining is required, the pool should be refilled as soon as the work is complete.

Is it normal to have to add water to my pool every week?

Yes. Pools naturally lose water through evaporation, splashing, and normal filtration. Adding water weekly helps keep the water level high enough for proper circulation. If the level drops unusually fast, it may indicate a leak.