When the evenings turn cold and the water temperature drops, it is time to plan for winter. The question how do you winterize a pool is not just about putting on a cover and switching off the pump. Proper winterization protects the pool structure, pipes, equipment, and water quality during months of frost, leaves, and precipitation. It also reduces the work when it is time to open the pool again in spring.
In Sweden, every pool owner needs to take into account a climate where temperatures can change quickly. A well-thought-out routine is therefore an investment in both the pool's lifespan and an easier swimming season next year.
When should the pool be winterized?
Winterize the pool when the water temperature is consistently around 10-12 degrees or lower. At that temperature, algae grow much more slowly, while the water is still warm enough for you to clean it and balance the chemicals effectively.
Closing too early can lead to unnecessary buildup and algae growth, especially during a mild autumn. If you wait too long, however, there is an increased risk that night frost will affect pipes, the heat pump, or other equipment. The exact timing varies across the country, but for many pools, September to November is relevant.
If you have a pool enclosure, the swimming season can often be extended, but the enclosure does not eliminate the need for winter closing. When swimming is finished and the temperature has dropped, the water, pipe system, and equipment must be secured.
How do you winterize a pool step by step?
A well-executed closing depends on the correct order. Always start with clean water and proper water chemistry. That gives the winter treatment the best conditions to work and helps you avoid trapping dirt under the pool cover.
Clean the pool thoroughly
Vacuum the bottom, brush the walls and steps, and empty the skimmer baskets. Remove leaves, pollen, and other organic material that would otherwise decompose over winter and burden the water. Also clean the waterline carefully. Grease, sunscreen, and dirt along the edge are easier to remove now than after several months under a cover.
Backwash the sand filter according to the system's instructions, or clean the filter cartridge if you have a cartridge filter. A clean filter ensures that the final circulation before closing is effective and gives you a better starting point for spring.
Adjust pH and disinfection
First check the pH level. For most pools, a pH between 7,2 and 7,6 is a good level before winter. An excessively high pH can contribute to scale deposits, while a low value can be stressful for certain materials and components.
Then shock chlorinate the water according to the dosage for your pool volume and the product you are using. Let the circulation system run so the treatment is distributed properly. The same principle applies to saltwater pools, but always follow the recommendations for your specific purification system and check the condition of the salt cell before shutting it down.
Once the chlorine level has stabilized, you can add winter treatment. Winter treatment is not a substitute for cleaning or balanced chemistry, but it helps prevent algae growth and buildup during the cold period. Dose according to the pool's water volume and avoid mixing products at random.
Lower the water level if needed
How much the water should be lowered depends on the pool type, inlets, skimmer, and the winter cover you use. In many pools, the water level is lowered below the inlets and skimmer to reduce the risk of frost damage. In other solutions, the water level may remain higher, provided that penetrations and pipes are properly winterized.
So there is no single water level that suits all pools. A PP pool, thermopool, glasfiberpool, and above-ground pool may have different conditions, as can pools with an integrated staircase, an overflow solution, or special built-in details. Always follow the instructions for your facility and your pool cover.
Do not empty the pool completely unless it is specifically designed for that. The water helps stabilize the pool against ground pressure and groundwater. In some cases, an empty pool can be subjected to greater loads than a properly winterized pool with water left in it.
Drain and frost-proof pipes and equipment
The most critical step is removing water from the parts that can freeze. Switch off the circulation pump, heat pump, and any additional equipment according to the manufacturer's instructions. Open drain plugs on the pump, filter, heater, and other components where water can remain.
Pipes should be blown clear using the proper method and equipment. Do not use a standard compressor without knowledge of the correct pressure - too much pressure can damage fittings, valves, and sensitive parts. Once the pipes are emptied, install winter plugs in the inlets and outlets. The skimmer and other exposed parts also need protection against ice formation.
If you have a pool heat pump, it should normally be drained of water and switched off according to its own manual. It is a good idea to cover the unit with a ventilated cover if the manufacturer recommends it, but never block airflow in a way that could create moisture problems.
Protect the pool against ice and precipitation
In an in-ground pool, winter floats, ice compensators, or other solutions are often used to reduce stress when the ice expands. They are particularly relevant in areas with recurring severe cold. Placement and quantity depend on the pool's shape and size.
A proper winter cover keeps leaves, dirt, and light out of the water. It makes a big difference to how the pool looks at spring opening. The cover should be properly tensioned, secured, and adapted for snow load and rainwater. A loose or improperly installed cover can collect water, reduce safety, and risk wind damage.
A pool enclosure is very practical protection for most of the year and helps keep dirt away. During the winter, you still need to check snow load, tracks, locks, and drainage. A pool enclosure is not automatically designed for unlimited amounts of heavy, wet snow. Therefore, brush the snow off carefully with a tool that does not scratch the surface, and avoid forcing enclosure sections that have frozen in place.
Common mistakes when winterizing a pool
The most common mistake is closing a pool with unbalanced or dirty water. That allows buildup, algae, and discoloration to take hold over winter. Another is simply switching off the pump without draining pipes and equipment. Even small amounts of water in the wrong part of the system can cause costly frost damage.
Many also underestimate the importance of proper protection. A standard tarp is rarely a long-term solution for a pool in a Swedish winter climate. It can collect rainwater, let in light, or lie directly against the water surface in a way that makes maintenance harder. A pool-specific winter cover provides a better fit, safer fastening, and cleaner water.
Also avoid leaving chemicals, test equipment, or sensitive technology unprotected outdoors. Store chemicals in a dry, cool, and child-safe place, separate from one another according to the product's instructions. Bring in loose parts such as the ladder, thermometer, and any robotic cleaner when appropriate.
When is professional winterization the right choice?
If you have an advanced pool installation with a heat pump, salt chlorinator, automatic dosing system, pool enclosure, or several water features, professional winter closing can be a wise reassurance. The same applies if you are unsure how the pipe system should be blown out or how your particular pool model should be handled.
A professional inspection reduces the risk of damage and creates a clear routine for the coming seasons. Pooltime can help with winterization for those who want the pool's equipment, water, and protection handled with the proper method.
Once the pool is closed, it is enough to check it from time to time. Make sure the cover is securely in place, that snow and standing water are not putting stress on the structure, and that no parts have been moved by the wind. That small check in the middle of winter may be what makes the first swim of spring feel close rather than far away.
