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What Should California Homeowners Do With Their Pools in Winter?

Table of Contents

Quick Overview

California’s winters are mild in many areas, but not everywhere. High deserts, mountain towns, and the Central Valley can see freezes. Coastal cities mostly face storms, debris, and cooler water. Because of this, there isn’t one winter plan for everyone.

Most homeowners choose one of three approaches:

  • Keep the pool open (“run light”): Leave it operational, reduce pump speed and runtime, keep water balanced, and use a cover when not swimming. This works well in coastal and low-freeze areas and pairs with variable-speed pumps.
  • Do a “soft close” (partial closing): Deep clean, balance chemistry, shock, cut circulation time, and cover the pool. Keep equipment ready to run if a hard freeze is forecast. Good for areas with occasional cold snaps or when you’ll be away.
  • Full winterization (colder zones): In high-elevation or consistently freezing locations, fully winterize: clean, balance, shock, lower the water if the builder calls for it, drain vulnerable equipment, and use an ASTM-rated safety cover.

Quick Decision Guide

Situation Best Choice Why It Helps
Coastal / Southern CA, few freezes Keep open or soft close Keeps water clear with minimal effort; lowest restart costs in spring; use lower pump speeds for energy savings.
Inland valleys with sporadic freezes Soft close Ready for cold snaps; freeze-protection modes keep water moving and reduce freeze risk.
Mountains / high desert (regular hard freezes) Full winterization Protects shell, tile, and equipment from freeze damage; use an ASTM F1346 safety cover.

If You Keep the Pool Open

Focus on clean water, safe chemistry, and efficient circulation.

  • Skim, brush, vacuum after wind or storms. Wildfire ash can land in pools; clean, rebalance, and avoid use until chemistry returns to normal.
  • Use a cover when not swimming. Covers cut leaf load and can reduce evaporation by up to ~95%, saving water and heat. A solar/thermal cover is not a safety device.
  • Run the pump slower and shorter. Cooler water slows algae growth. Variable-speed pumps at lower RPMs can slash power use.
  • Chemistry targets: keep pH 7.0–7.8 and free chlorine typically 1–4 ppm (often ≥2 ppm if using cyanuric acid). Test after storms and before/after shocking.
  • Freeze forecasts: enable automation’s freeze-protection to circulate water during cold snaps.

If You “Soft Close” (Partial Closing)

  1. Deep clean: net, brush, vacuum; empty baskets.
  2. Backwash/clean the filter.
  3. Balance water and shock (see “Should You Shock Before Winter?”).
  4. Dial back circulation but keep freeze mode or alerts for cold nights.
  5. Cover the pool: safety cover if you want a barrier; solar/thermal cover for evaporation/heat control.

Full Winterization (For Routine Freezes)

  • Clean thoroughly, balance, and shock.
  • Lower water level per builder instructions (often below skimmer/tile line).
  • Blow out and plug lines; drain equipment (pump, filter, heater, chlorinator) and open air reliefs.
  • Install an ASTM F1346 safety cover.

If power fails during a freeze: turn off breakers, open drains/relief valves, remove pump/heater drain plugs, and protect exposed equipment so trapped water cannot freeze inside housings.

Regulations & Standards in California for 2025 and 2026

  • No statewide rule to “winterize.” The law focuses on safety barriers, compliant safety covers, anti-entrapment, and energy-efficient pumps. Local water and discharge rules also apply.
  • Safety barriers and covers: The California Swimming Pool Safety Act (single-family homes) requires at least two drowning-prevention features when building or remodeling. Safety covers must meet ASTM F1346.
  • Energy rules for pumps: Since July 19, 2021, dedicated-purpose pool pumps and replacement motors must meet federal efficiency standards. Replacement motors ≥0.5 THP are typically variable-speed. Freeze-protection defaults are capped to avoid waste.
  • Water conservation: State conservation rules in 2025 work through local suppliers. Many recommend—and during drought phases some require—pool covers to reduce evaporation. Check your city or water district.
  • Pool water disposal: Cities vary. Some allow fully dechlorinated, pH-balanced pool water to storm drains; others require discharge to a sanitary sewer cleanout. Always verify local rules.
  • Wildfire ash guidance: County health departments provide steps for cleaning pools after ashfall; do not use the pool until cleaned, filtered, and rebalanced.

Should You Shock Before Winter?

Yes—if you’re soft-closing or fully closing. Shocking suppresses algae and bio-growth when the pool will run less.

  • What to use: fast-acting oxidizers such as liquid chlorine (sodium hypochlorite), calcium hypochlorite (cal-hypo), or a non-chlorine shock (potassium monopersulfate) per label directions. Trichlor tablets are not used for shocking; they dissolve slowly and add stabilizer.
  • When it’s safe to swim: wait until free chlorine is back to 1–4 ppm and pH is 7.0–7.8. Test to confirm.
  • Safety: read labels, wear eye/hand protection, never mix different chlorines, and always add chemical to water (not water to chemical).

Please Don’t Drain Your Pool “for Winter”

Fully draining a pool in California is usually unnecessary and risky. Empty shells can float or crack from groundwater pressure, especially during or after storms. If a partial drain is needed—such as lowering high stabilizer (CYA)—consult a licensed pro and follow the builder’s instructions.

If you must lower water, choose dry weather, use relief valves if designed for your pool, refill promptly, and follow local discharge rules (dechlorinate and verify pH; many cities prefer sanitary sewer cleanouts).

What Winter Choices Mean for Homeowners

  • Lower bills and fewer spring surprises: Balanced, covered pools reduce algae blooms, refills, and heater runtime. Biggest savings lever: lower pump speeds with a variable-speed pump.
  • Avoid preventable damage: Freeze bursts (more likely inland/high elevation), popped shells from ill-timed draining, and storm debris are expensive. Freeze protection, covers, and avoiding drains during wet periods reduce risk.
  • Liability still matters in winter: Maintain code-compliant barriers and, if you want the cover to serve as a barrier, make sure it meets ASTM F1346. Many homeowners also increase personal liability limits or add an umbrella policy—ask your agent.

Frequently Asked Points

Do I have to winterize by law in California? No. Codes focus on barriers, safety-rated covers (if used), anti-entrapment, and efficient pumps. Local water and discharge rules also apply.

Is a solar/thermal cover a safety cover? No. It helps reduce evaporation and heat loss but is not a safety barrier. Safety covers must meet ASTM F1346.

How long should I run the pump in winter? Run as little as needed to keep water clear and mixed. Lower speeds save energy. Increase runtime after storms or heavy debris.

What if power goes out during a freeze? Turn off breakers, open drains on pump/filter/heater, and protect equipment until temperatures rise or power returns.

Can I send pool water to the street gutter? It depends on your city. Many require dechlorination and pH checks; some require discharge to the sanitary sewer. Always check local guidance.

Step-by-Step Winter Checklist

  1. Weekly (or after storms): skim/brush/vacuum; empty baskets.
  2. Chemistry: keep pH 7.0–7.8; maintain free chlorine about 1–4 ppm (often ≥2 ppm with CYA). Test after rain or ashfall.
  3. Cover: use whenever not swimming; choose a safety-rated cover if you want it to serve as a barrier.
  4. Circulation: reduce speed/time for savings; ensure freeze mode is enabled if relevant.
  5. Shock before long idle periods: liquid chlorine, cal-hypo, or non-chlorine shock; do not use trichlor tablets to shock. Wait for chlorine to return to normal range before swimming.
  6. Disposal: if you must drain some water, dechlorinate and follow local discharge rules.

Sources and Further Reading