Pool closing · Texas
When to Close Your Pool in San Antonio, TX: Deadline, Window & Checklist
Last updated: July 15, 2026 · Model window year: 2026 · dates · checklist · FAQ
Plan to close your San Antonio pool by November 21. The local 7-day mean temperature drops out of the algae-risk zone around November 12, and NOAA normals put the first 32°F freeze near November 28 — winterize between those dates and the water goes under the cover cold, clean, and easy to reopen. Below: today's water estimate, the full closing window, and a step-by-step winterizing checklist.
San Antonio closing dates at a glance
| Closing window | November 12 – November 21 |
|---|---|
| Close by (deadline) | November 21 |
| First freeze, 50% probability | November 28 |
| Open by (recommended) | February 25 |
| Opening window | February 18 – March 11 |
| 61°F crossing (7-day mean) | March 11 |
| Swim-season length (80°F+ days) | 192 days |
| NOAA normals station | San Antonio Incarnate Word · 3.1 mi · 700 ft |
Closing is close to optional here — many San Antonio owners trade the cover for shorter pump hours and swim the shoulder seasons. If you do close, the late window above still applies.
The same model in water terms: San Antonio's estimated pool temperature runs about 68°F in mid-April, 81°F in mid-June, 85°F in mid-August, and 73°F in mid-October, peaking near 85°F. Those four checkpoints — not any calendar holiday — are what the windows above are protecting.
The 12-step San Antonio winterizing checklist
The order matters more than the date: balanced water first, verified-dry lines before anything else freezes-proofs, and the cover only after everything below it is done. Work the list inside the window above.
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Balance the water a few days ahead
Start midweek for a weekend close: bring alkalinity and pH into their label ranges and let the water settle. What you seal under the cover is what the pool soaks in until spring.
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Deep-clean the pool
Make the last cleaning the best one of the year: full skim, full brush, careful vacuum. Debris left behind steeps all winter and greets you as April's water problem.
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Service the filter one last time
One final filter service per the manual — cartridges rinsed and stored dry indoors, sand or DE backwashed. Winter turns trapped gunk into concrete.
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Apply winter chemicals per label
Add a winterizing kit or your usual closing chemicals exactly as their labels direct for your volume, with the pump still circulating so everything distributes before shutdown.
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Lower the water level
Your cover's manual sets the number — commonly a few inches under the skimmer for solid covers, barely below normal for mesh. Stop there. The remaining water isn't laziness; it's ballast holding the shell in the ground.
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Blow out the lines and plug returns
Work line by line: push air until the return spits dry mist, plug it against the flowing air, move on. Skimmer, returns, cleaner line, in whatever order your plumbing prefers — dry pipes are the entire point of closing.
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Protect the skimmer
Give the skimmer something cheap to break: a guard bottle or rated plug absorbs the ice expansion that would otherwise split the housing.
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Add pool antifreeze where blowouts fall short
If any line can't be verified dry, add pool-grade antifreeze per its label. Use only pool antifreeze — automotive products don't belong in pool plumbing.
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Drain the equipment
Every vessel on the pad — pump, filter, heater, chlorinator — gets its drain plugs pulled. Drop all the plugs in the pump basket; that's the one place everyone looks first in spring.
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Set the air pillow and cover
Pillow first, cover second, tension last. A properly centered pillow turns the winter ice sheet from a wall-pressing ram into a harmless dome.
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Store chemicals properly
Seal opened containers, keep oxidizers and acids separated, and store everything cool, dry, and locked away from kids and pets — exactly as each label describes.
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Winterize the water features
Waterfalls, slides, and spillover spas hold water in places gravity won't clear — blow those lines separately and plug them, or they'll be the one crack you find in spring.
What to buy before the rush
A small stack of supplies turns the checklist above into a single-weekend job. Buy before San Antonio's November rush and the whole list ships at leisure instead of sprinting.
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Air pillow
Gives ice somewhere to push besides your pool walls.
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Winter cover
The one purchase every other closing step depends on.
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Cover pump
Keeps rain and melt off a solid cover all season.
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Expansion plugs + skimmer guard
Cheap rubber that stands between ice and your fittings.
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Pool antifreeze
For lines you can't verify dry — pool-grade only, per label.
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Winter closing kit
Season-length winter chemicals in one label-dosed box.
How San Antonio compares locally
San Antonio closes in the earlier half of Texas's calendar. Neighbors run close: New Braunfels (30 mi away) models its deadline at November 11 (about a week earlier vs San Antonio's November 21), while San Marcos (45 mi) shows November 21. The spring mirror of this page is the San Antonio opening guide, and the season overview draws both windows on a single bar.
The instrument behind this page is San Antonio Incarnate Word, 3.1 miles east of San Antonio — the closest station publishing complete 1991–2020 daily temperature normals. Thirty years of its readings set every date above; your own yard adds or subtracts a degree with shade, wind, and pavement, which is what the window's width is for.
Field notes for San Antonio owners
Match the drainage plan to the cover
Solid covers shed nothing — they need a cover pump staged before the first storm and checked after each one. Mesh covers drain themselves but pass silt that settles all winter. Either way, the plan is decided in October, not improvised in January when the cover is an ice sheet.
Salt cells overwinter indoors
Remove the cell at closing, inspect and clean per the manufacturer, and store it inside with the unions capped. A dummy cell or spacer keeps the plumbing sealed. Cells left in outdoor plumbing through freezes are a common — and completely avoidable — spring casualty.
Cold water is the whole point
A pool closed at 55°F barely changes all winter: algae are dormant, chemicals hold, and spring opens with a light dusting instead of a bloom. A pool closed at 72°F runs its own quiet ecosystem under the cover for a month. The date matters less than the water temperature it represents.
Don't close a pool people are still using
With San Antonio's long season, the question isn't "is it November?" but "has the water actually cooled?" The window running to November 21 exists because warm-water closings breed spring algae. If swimmers keep showing up through November, let them — patience here is free maintenance.
San Antonio pool closing FAQ
What temperature should water be to close a pool?
Cold enough that biology has clocked out — below 65°F and falling, ideally low 60s. The widget above tracks San Antonio's actual water; the normals say the durable cool-down arrives near November 12, and anything inside the window to November 21 closes clean.
Can you close a pool too early?
Early closing is the mistake the whole model is built to prevent from the other direction. A cover installed over 70°F water is a terrarium: sanitizer decays, algae compound, nobody looks for months. San Antonio's water isn't reliably out of that zone until about November 12 — the calendar's first cold weekend doesn't change that.
Do I need antifreeze in pool lines?
Only for lines you can't verify dry — a proper blowout makes antifreeze unnecessary. Where doubt remains, use pool-grade product at its label rate, never automotive. No freeze-probability normal is published near San Antonio, so let the live forecast, not a calendar, tell you when freeze protection starts mattering.
How far should I drain my pool for winter?
As far as your cover manufacturer specifies and no farther — typically a few inches below the skimmer mouth for solid covers, near normal level for many mesh systems with skimmer plugs. Never drain fully: an empty shell can shift or crack under groundwater pressure.
What happens if you don't winterize a pool?
In a freeze climate, physics wins: water expands about 9% when it freezes, cracking pump housings, filter tanks, heat exchangers, and pipes. With San Antonio's first 32°F night arriving near November 28 in the normals, an unwinterized pad is a spring repair bill waiting to be discovered.
When is the last safe date to close in San Antonio?
The model draws the line at November 21 for San Antonio. It isn't arbitrary: a week of margin before the November 28 first-freeze normal, and the whole closing sequence needs a working weekend of margin. The one exception that overrides any date — a hard freeze inside the 10-day forecast, which the widget above flags as urgent.
Email me when San Antonio hits the closing window
Data: NOAA 1991–2020 climate normals via San Antonio Incarnate Word (3.1 mi); live outlook by Open-Meteo. Full attribution on the sources page. Model assumptions and error bars on methodology.