How Long Can a Pool Be Empty? Safe Duration & Risks

First, Let's Diagnose Your Situation

The honest answer for an inground pool: this isn't really a calendar question, it's a groundwater question. A full pool's water weight is what holds the shell down against hydrostatic pressure from groundwater pushing up underneath it. Drain it, and under a high water table or after heavy rain that pressure can crack the shell or float it out of the ground — sometimes within a day, not weeks. So the safe rule isn't a number; it's this: don't fully drain an inground pool unless you have a specific reason and controlled conditions, and keep it full the rest of the time. The figures below are best-case ceilings that assume low groundwater and dry weather — treat them as upper limits, not green lights.

The most important diagnostic question is: what type of pool do you have? Inground concrete/plaster pools face the highest risk when empty, while vinyl liner and fiberglass pools have different concerns. Above ground pools generally handle being empty much better than any inground option.

Safe Duration by Pool Type

Inground Concrete/Plaster Pools

Best case: about 1-2 weeks — and only with low groundwater and no rain in the forecast. Under a high water table or after heavy rain it can be far less, even the same day. Don't drain a concrete pool without a specific reason and a plan to refill promptly.

Concrete pools face the greatest risk when empty due to hydrostatic pressure from groundwater. When your pool is full, the water weight counteracts upward pressure from groundwater beneath the pool. Once empty, this pressure can cause the pool shell to literally pop out of the ground or crack severely.

Signs of hydrostatic pressure problems include:

• Visible cracks appearing in the pool shell
• Pool floor showing signs of lifting or buckling
• Water seeping up through deck drains or cracks
• Pool equipment shifting or moving

Vinyl Liner Pools

Draining usually means replacing the liner. An empty vinyl pool can still float or shift with groundwater, but the bigger catch is the liner itself: once drained, an older liner typically shrinks and won't reseat, so emptying the pool often means buying a new liner. That's why vinyl pools are normally only drained when the liner is being replaced. UV also degrades an exposed liner quickly. If you don't need a new liner, don't drain it.

Fiberglass Pools

Don't fully drain a fiberglass pool yourself — check with the builder or dealer first. Fiberglass shells rely on the water inside to brace their shape, so a drained shell can float or pop out of the ground readily, and the walls can bulge or deflect inward without water supporting them. Many manufacturers require an authorized dealer to drain the pool (doing it yourself can even void the warranty). If it genuinely must be drained, do it with professional guidance and only as briefly as groundwater conditions allow.

Above Ground Pools

Structurally fine for a long time—but the liner is the real limit.

Above ground pools handle being empty far better than any inground type because they're not fighting groundwater pressure, so the frame and walls can sit empty for an extended period. The catch is the vinyl liner: exactly like an inground vinyl pool, a drained liner can shrink, won't reseat, and UV-degrades quickly in the sun. If you want to keep the existing liner, don't leave the pool empty and sun-exposed for more than a week or two—shade or cover it—or plan on installing a new liner when you refill.

Environmental Risk Factors

High Groundwater Areas

If you live in an area with high groundwater (near lakes, rivers, or naturally wet soil), reduce all timeframes by 50%. These conditions create much higher hydrostatic pressure risks. You can identify high groundwater areas by:

• Neighbors having sump pumps
• Basement flooding being common in your area
• Shallow wells (less than 20 feet deep)
• Standing water in yards after rain

Weather Considerations

Rainy seasons dramatically reduce safe empty time. Heavy rainfall increases groundwater levels and hydrostatic pressure. If significant rain is forecast, either refill immediately or install a hydrostatic relief valve system.

Extreme heat also accelerates liner damage and increases evaporation from surrounding soil, potentially causing ground settling around the pool.

Solutions for Extended Empty Periods

Hydrostatic Relief Valve Installation

For pools that must stay empty longer than recommended timeframes, install hydrostatic relief valves in the main drain. These valves automatically open when groundwater pressure builds up, allowing water to enter the pool and equalize pressure. This solution works for concrete and fiberglass pools but requires professional installation.

Partial Filling Strategy

Instead of completely emptying, maintain 12-18 inches of water in the shallow end. This mainly protects the liner and keeps the shallow-end surface from drying and cracking in the sun, and adds some ballast — but it does NOT replace relieving groundwater pressure: against a high water table you still need the hydrostatic relief plug opened, since a foot or so of shallow water is not enough weight to stop a determined uplift. Add liquid chlorine as needed to keep that shallow water sanitized and prevent algae—test and adjust, since shallow water sitting in the sun loses chlorine fast (check every few days rather than weekly). For a closer dosing estimate, use our all-in-one pool calculator.

Groundwater Monitoring

Have a professional install a monitoring well near your pool to track groundwater levels. If groundwater rises to within 2 feet of your pool floor, refill immediately regardless of your original timeline.

Emergency Refill Procedures

If you notice any signs of structural stress, begin refilling immediately:

1. Start filling right away to get water weight back onto the pool floor evenly (don't worry about fill order to avoid 'air locks'—those are cleared at the pump and skimmer, not by how you fill the basin)
2. Fill continuously until pool reaches normal operating level
3. Monitor for continued cracking or movement during filling
4. Call a structural engineer if damage is visible

Warning: Never attempt to push a lifted pool floor back down. The forces involved can cause catastrophic failure.

Prevention and Planning

Before emptying your pool:

• Check local weather forecasts for the next 2-3 weeks
• Consult your pool builder about hydrostatic pressure history in your area
• Plan work to minimize empty time - have all materials and contractors ready
• Consider partial draining instead of complete emptying when possible
• Install hydrostatic relief valves if extended emptiness is necessary

When Professional Help Is Needed

Call a pool professional immediately if:

• Your pool has been empty longer than recommended timeframes
• You notice any structural changes or cracks
• Water is seeping up around the pool
• Equipment has shifted position
• You're unsure about groundwater conditions in your area

The cost of professional consultation is minimal compared to potential structural repairs, which can easily reach $10,000-50,000 for severe hydrostatic pressure damage.

For the full breakdown of safe chlorine levels by CYACyanuric Acid (stabilizer) — Sunscreen for your chlorine — it keeps sunlight from burning it off. The catch: the more you have, the more chlorine you need to keep. learn more → level, see our pool water chemistry guide.

Recommended for this job

Taylor K-2006C Complete FAS-DPD Pool & Spa Test Kit The FAS-DPD kit pool pros trust — reads chlorine accurately even at shock/SLAM levels, plus pH, alkalinity, calcium hardness and CYA. View on Amazon →

Affiliate links — we may earn a small commission at no extra cost to you.

Switch to Salt Water

Softer water. No more chlorine tabs.

Shop salt systems →onamazon

Sponsored