How to Winterize Your Swimming Pool

As winter approaches, it's time for winterizing — the process of preparing your home, car, and yard for harsh cold. One home feature that absolutely requires it is your swimming pool. Properly winterizing your pool protects it from freeze damage to the plumbing and equipment, prevents algae growth, and ensures you open to clear, swimmable water in spring rather than a green, damaged mess. You can start as early as autumn, before the first freeze. While it takes some effort, doing it right saves you money and a miserable spring cleanup. Here's a step-by-step guide to winterizing your swimming pool.

Clean the pool thoroughly

The first step is to clear the pool of all debris and contaminants. Use nets, your pool's filters, and a pool skimmer net on a pole to remove leaves, dirt, and anything floating or settled. Brush the walls and floor and vacuum the pool to remove dirt and the beginnings of algae. A clean pool going into winter is far less likely to develop problems over the closed months, and it makes opening in spring much easier. Don't skip this — closing a dirty pool traps debris and organic matter that feed algae and stain surfaces all winter, undoing much of the benefit of winterizing.

Balance the water chemistry

Before closing, balance your pool's water chemistry to protect the surfaces and prevent problems over winter. Test and adjust the pH, alkalinity, and calcium hardness to the proper ranges, and shock the pool to kill any bacteria and algae. Properly balanced water won't corrode or scale your pool's surfaces and equipment during the months it sits unused, and the right sanitizer levels prevent algae and bacteria from taking hold. A pool winterizing chemical kit bundles the products you need to close the pool correctly. Getting the chemistry right at closing is one of the most important steps for a clean, undamaged spring opening.

Lower the water level

In climates that freeze, lower your pool's water level below the skimmer and return lines (typically to the guidance for your pool type and cover). This is important because water expands when it freezes, and water left in the skimmer and lines can crack them. Don't drain the pool completely, though — a fully empty pool can be damaged by ground pressure or "pop" out of the ground in some cases, and the water provides some support. Lower it to the correct level for your setup and cover, no more. Getting the water level right protects your plumbing from freeze damage while keeping the pool structurally safe.

Protect the plumbing and equipment

Freezing water in the pipes and equipment is what causes the most expensive winter pool damage, so protect them. Drain water from the pump, filter, heater, and chlorinator according to your equipment's instructions, and remove drain plugs. Blow out the plumbing lines to clear water from them, then plug the lines (special winterizing plugs) to keep water out. Add non-toxic pool antifreeze to the lines as extra insurance against any remaining water freezing. This is the most technical step and the most important for preventing costly damage — if you're unsure, this is the part worth getting right or having a professional handle. Protected plumbing is the heart of pool winterizing.

Add winterizing chemicals and accessories

To keep the water clean over the closed season, add winterizing chemicals — a winter algaecide and possibly a floater with slow-release sanitizer help prevent algae and keep the water clearer until spring. Some people add an enzyme product to break down organic contaminants. These chemicals work over the long closure to fight the algae and buildup that would otherwise turn your pool green. Following the winterizing kit's instructions for what to add ensures your water stays in the best possible condition through months of sitting covered, making your spring opening dramatically easier and cleaner.

Cover the pool securely

Finally, cover the pool with a quality winter pool cover to keep out debris, leaves, and contaminants, and to block sunlight that promotes algae growth. Make sure the cover is secure and fits properly — a loose or damaged cover lets debris in and can be blown off in winter storms. Use water bags, cover clips, or a safety cover anchored properly depending on your cover type. A secure cover is your pool's main defense over winter, keeping the clean, balanced water you've prepared protected from everything the season throws at it. Check periodically through winter that the cover remains secure and clear of excessive water or snow load.

Check on it through winter

Winterizing isn't entirely "close and forget." Through the season, periodically check that the cover is secure and remove any heavy accumulation of water, leaves, or snow from on top of it (a cover pump helps drain rainwater). In milder winters, you may occasionally check the water and add chemicals if needed. A little monitoring catches problems — a slipped cover, debris buildup — before they become bigger issues. This light upkeep protects all the work you did closing the pool, ensuring it stays in good condition until you're ready to open it again in spring.

What I'd skip

Skip closing a dirty pool — debris and organic matter feed algae all winter. Skip leaving water in the skimmer, lines, and equipment, which freezes and cracks them. Skip draining the pool completely, which can cause structural damage. And skip a loose or poor cover; a secure, quality cover is your pool's main winter defense.

The honest answer

Winterizing your swimming pool protects it from freeze damage and algae so you open to clear water in spring: clean it thoroughly, balance the chemistry and shock it, lower the water below the skimmer, protect the plumbing and equipment from freezing (the most important step), add winterizing chemicals, and cover it securely. Start in autumn before the freeze, check on it through winter, and you'll prevent the cracked pipes and green-pool nightmare that catch unprepared pool owners. A weekend of proper closing saves a fortune in repairs and a miserable spring cleanup.