Pool closing · California
When to Close Your Pool in Brentwood, CA: Deadline, Window & Checklist
Last updated: July 15, 2026 · Model window year: 2026 · dates · checklist · FAQ
Target November 10 as the practical closing deadline in Brentwood. Our model of NOAA 1991–2020 normals keeps the 7-day mean above 61°F until October 31; after that, cooling water winds algae down while you work the checklist below. The hard stop is equipment freeze damage — normals put Brentwood's first 32°F night near December 19.
Brentwood closing dates at a glance
| Closing window | October 31 – November 10 |
|---|---|
| Close by (deadline) | November 10 |
| First freeze, 50% probability | December 19 |
| Open by (recommended) | April 3 |
| Opening window | March 27 – April 17 |
| 61°F crossing (7-day mean) | April 17 |
| Swim-season length (80°F+ days) | 142 days |
| NOAA normals station | Antioch Pumping Plt #3 · 3.8 mi · 60 ft |
A classic four-season pool calendar: open early into cold water, close late into cold water, and Brentwood's 142 days of prime swimming sit safely in between.
Put dates aside and follow the water: the Brentwood curve says roughly 60°F by mid-April, 72°F by mid-June, 76°F in mid-August, then back down through 68°F in mid-October. The summer ceiling sits near 76°F, and every window above is just a line drawn on this curve.
The 12-step Brentwood 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
Do the chemistry midweek, close on the weekend: alkalinity and pH into label ranges with days of circulation left to spread them. Winter locks in whatever state the water holds on closing day.
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Deep-clean the pool
Leave nothing organic behind: skim the surface, brush every wall and step, vacuum the floor slowly. What goes under the cover dirty comes out worse — winter only ever compounds what it's given.
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Service the filter one last time
Send the filter into winter clean: backwash the sand or DE, rinse and dry the cartridges indoors. Media stored dirty over winter hardens into a spring problem no backwash fixes.
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Apply winter chemicals per label
Run the winter kit through moving water: dose each product per its label with the pump on, give it a few hours to distribute, then start the shutdown. Chemistry added to still water stays where it lands.
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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
The blowout is the whole ballgame: drive air through each line until it runs dry, seat the plug against the airflow, move to the next. A dry line cannot burst, full stop.
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Protect the skimmer
Seat a skimmer guard or bottle in the throat — ice that forms there needs a sacrifice, and a two-dollar bottle beats a plumbing repair under the deck.
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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
Float a centered air pillow, then land the cover and secure it the way its design intends — bags, cable, or straps. Ice sheets need somewhere to collapse inward, and the pillow is that somewhere.
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Note this year's dates
Jot down when Brentwood's water actually cooled and when you closed. A two-line note beats memory next October 31 — your own yard runs a few days off any model, including ours.
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Calendar the off-season checks
Set a monthly reminder from November 10 to spring: check cover tension, pump off standing water, and glance at the water level. Fifteen minutes a month protects the whole closing job.
What to buy before the rush
A small stack of supplies turns the checklist above into a single-weekend job. Buy before Brentwood's October rush and the whole list ships at leisure instead of sprinting.
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Winter closing kit
Season-length winter chemicals in one label-dosed box.
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Air pillow
Centers under the cover so ice pushes inward, not outward.
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Winter cover
The one purchase every other closing step depends on.
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Cover pump
Solid covers collect rain all winter; this is the drainage plan.
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Expansion plugs + skimmer guard
The blowout's finishing move — one per return, one for the skimmer.
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Pool antifreeze
Pool-rated glycol for the lines air couldn't clear.
How Brentwood compares locally
Brentwood closes in the later half of California's calendar. Neighbors run close: Antioch (5 mi away) models its deadline at November 10 (the same day vs Brentwood's November 10), while Pittsburg (11 mi) shows November 10. The spring mirror of this page is the Brentwood opening guide, and the season overview draws both windows on a single bar.
Every number on this page traces to one instrument cluster: Antioch Pumping Plt #3, 3.8 miles northwest of Brentwood's center at an elevation near 60 feet. NOAA computed its 1991–2020 normals from roughly three decades of daily readings — long enough that one strange spring in Contra Costa County barely moves the dates.
Field notes for Brentwood owners
Leaf season vs closing day
If your yard drops serious leaves, the cheap trick is a leaf net over the main cover through the drop, then one bulk removal before snow. Leaves that winter on (or worse, under) the cover steep like tea and hand you stained water and clogged pumps in spring.
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.
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.
Brentwood pool closing FAQ
What temperature should water be to close a pool?
Close once water holds below about 65°F — the point where algae go mostly dormant — and before hard freezes. In Brentwood, the 7-day mean drops through the threshold around October 31, so the window between then and November 10 is the sweet spot for a clean, stable close.
Can you close a pool too early?
Yes — it's the most common closing mistake. Seal 70°F water under a cover and algae keep growing in the dark all autumn; the spring opening turns green and expensive. In Brentwood, hold off until the cool-down near October 31 before covering.
Do I need antifreeze in pool lines?
Treat antifreeze as a backup, not a substitute: the real protection is air in dry lines. Where a full blowout isn't possible, pool-grade antifreeze per label is cheap insurance against a cracked pipe — worth it anywhere freezes are routine, and Brentwood sees them from about December 19.
How far should I drain my pool for winter?
Only to the line your cover manufacturer prints — a few inches below the skimmer for most solid covers, close to operating level for many mesh designs with the skimmer plugged. The water you leave in is structural: it holds the shell against groundwater all winter.
What happens if you don't winterize a pool?
Expect equipment damage first — cracked pump volutes, split filter tanks, ruptured heater exchangers — then plumbing leaks that surface at startup. In Brentwood, normals put the first freeze near December 19; everything after that date is borrowed time for an unwinterized system.
When is the last safe date to close in Brentwood?
November 10, by our model — the cool-down plus ten days (the freeze normal, December 19, leaves room to spare). Later closes happen, but they happen in gloves. The winterizing steps above take a weekend; leave yourself at least that much runway before Brentwood's first freeze-risk stretch.
Email me when Brentwood hits the closing window
Data: NOAA 1991–2020 climate normals via Antioch Pumping Plt #3 (3.8 mi); live outlook by Open-Meteo. Full attribution on the sources page. Model assumptions and error bars on methodology.