Can I leave my pool covered for the winter in Arizona?

By Tom Bohner, founder of Solar Safe Pool Covers, an Arizona licensed contractor (CR-6 ROC #316530) manufacturing and installing custom pool covers in Phoenix & Tucson since 2002.

When to Cover for the Season in Arizona

Arizona is not one climate. Timing depends on your elevation more than the calendar.

These are starting points, not deadlines. A PowerLock can go on any week of the year, and plenty of low-desert customers cover in September simply because they are done swimming and want to stop paying to run the pool.

Option 1: Hibernate the Pool with a PowerLock

Hibernation is the part most Arizona pool owners do not realize is available to them. A solid vinyl safety cover blocks sunlight and seals off more than 90% of evaporation, and sunlight is what drives both algae growth and chlorine burn-off. Take the sun away from balanced water and the pool simply sits there. Not for a weekend. For months, or for years.

This is the single most common reason snowbirds, second-home owners, and families who are tired of the pool buy a PowerLock instead of filling the pool in.

How to hibernate an Arizona pool

1. Clean the pool thoroughly. Brush, vacuum, and skim. Anything organic left on the floor is what you will be looking at in March.
2. Bring the water to its normal level, about halfway up the skimmer opening or the middle of the top row of tile. A floating cover needs the water beneath it for support.
3. Balance every chemical, not just chlorine. Free and total chlorine 1.0 to 3.0 ppm, pH 7.2 to 7.8 (7.4 is ideal), total alkalinity 80 to 120 ppm, cyanuric acid 50 to 100 ppm, calcium hardness 250 to 500 ppm, TDS under 1,200 ppm.
4. Add a phosphate reducer and drive phosphates toward zero. Phosphates are algae food, and this is the step people skip.
5. Do not shock and then immediately cover. Heavy chlorine concentration sitting against the underside of a cover damages the material. Circulate first.
6. Put the cover on and lock every anchor. A partially anchored cover does not meet the ASTM F1346-91 safety standard.
7. Shut off the pump and filter. That is the step that stops the bills.

Through the winter, there is essentially nothing to do. Top the water off once or twice a year if you do not have an auto-leveler, and pump standing water off the cover after a storm. When you are ready to swim again, re-test and adjust the chemistry, then filter the full volume of the pool at least twice, roughly 24 to 48 hours, before anyone gets in.

What hibernation actually saves

• Chemicals: a covered pool typically needs up to 80% less chlorine, because UV burn-off is the main reason Arizona pools consume it.
• Water: solid vinyl seals off roughly 95% of evaporation. An uncovered Phoenix or Tucson pool loses close to 6 feet of water a year.
• Electricity: the pump is off, and the pump is usually the largest single electrical load in an Arizona backyard.
• Service: many customers drop their pool service company entirely for the season, or permanently.

Between those four, a PowerLock typically pays for itself in two to three years. Savings vary pool to pool, so treat these as ranges rather than promises.

Option 2: Keep Swimming with a HeatSaver

If you heat your pool or spa, winter is the season the HeatSaver was built for. It is a true insulating blanket, not a bubble cover: a cross-linked closed-cell polyethylene foam core sandwiched between two layers of 1600-denier woven fabric, independently tested at an R-value of about 1.8.

The reason that matters is where heated pools lose their heat. It is not through the walls. It is off the surface overnight, mostly through evaporation. A HeatSaver cuts evaporation by roughly 90% and retains up to 90% of the pool’s heat, so a covered pool typically drops only 1 to 3 degrees overnight instead of the much larger loss an open pool takes on a cold desert night.

Cut the overnight loss and your heater stops spending every morning re-heating water it already heated yesterday. That is where up to 75% lower heating costs comes from. It is also why we run an ASHRAE-based savings analysis with your actual location and utility rate before quoting, rather than asking anyone to take the number on faith.

Which One for Your Winter?

What Not to Do

A few pieces of standard winterizing advice are actively wrong for an Arizona pool with a floating cover:

• Do not drain the pool. A PowerLock floats and needs the water underneath it for structural support. Low water also puts strain on the cover and the anchoring system during storms.
• Do not chase a high chlorine reading. Under a solid cover with no UV, 1.0 to 3.0 ppm is the target. Running chlorine high does not help and shortens cover life.
• Do not leave standing water sitting on the cover. Use the included cover pump. Water on top of the cover is a drowning hazard, and a cover is never a substitute for supervising children.
• Do not skip the anchors. Every locking anchor, every time, or the cover is not rated as a barrier.

The Short Version

Leaving your pool covered all winter in Arizona is not just allowed, it is the least expensive and safest way to get through the season. Cover it to hibernate and stop paying to run a pool nobody is swimming in, or cover it to hold heat and keep swimming for a fraction of the heating cost. The only bad option is an open pool sitting there evaporating, burning chlorine, collecting debris, and staying open to a child or a pet all winter.