10 November 2022

Winterisation: How to Prepare Your Natural Pool for the Winter

With the best of a British summer moving into autumn, the sounds of splashing water and clinking glasses by the pool start to die down…


Because the winter to come is far too cold and grizzly for many to be thinking about their outdoor pools.

So, just turn it off and wait ‘till next season right?

Well, actually NO! There are many things that need to be done in order to prepare the pool for this period, thus preventing unnecessary damage which will be more expensive and time-consuming to fix when it is reopened in the next season.

Pools can be ‘passively’ winterised (where the pump operates on an idle setting) in climates where the temperature doesn’t drop below 5°C… But alas this is not the case in the hardy British Isles. As temperatures typically range between 2-7°C and drop to below 0°C, it is important to ‘actively’ winterise, which involves extra steps such as partial drainage.

When water freezes it expand up to 10% in volume, which can be just enough to crack open plastic and metal seals. This can create damage to expensive components, and even lead to a leaky system, so it is important to decrease the water level to just below the skimmers, and remove water from pipes and components above this level. Floats can be used at surface and submerged levels to relieve pressure from pool edges where deemed necessary during surface freezing.

As we are likely to expect a drop of rain over the winter (massive understatement!) the water will become diluted. Also, cold water is more corrosive to components and liners, and for these reasons, the pH of the pool needs to be accurately adjusted to make it more alkaline (pH 7.6-7.8).

As you can see from this pool we opened up at the start of the season, not shutting your pool down correctly can lead to a drastic clean-up process. It is important to note here that the customer tried to shut this pool down and not us…

This can of course be fixed, as you can see from the image below, but as the water chemistry needs to be adjusted incrementally it took many more revisits than usual before we restored it to its former glory.


Anyway, the pool must be thoroughly cleaned and filtered, as any debris will encourage algae growth, which we especially don’t want happening inside any of the pipeworks! This will include removal of debris, thorough scrubbing of walls and the bottom of the pool, and backwashing of the filter. Pool accessories such as fittings, toys, and baskets must also be cleaned and sanitised.

A ‘shock’ dose of chlorine should be calculated for your pool volume and carefully added wearing goggles and gloves (this stuff burns!), in order to keep the water sanitized for this long period of time. 

Once this is stabilised, long-lasting algaecides must be added, but periodical removal of debris and water composition checks and are also recommended. If you have a winter cover, now is the time to put this on.

Pumps, filters, and other components are now drained, and new filter media can be added in preparation for the new season.

Got all of that? Well, if you’d prefer us to professionally winterise your pool while you relax by the fire with a hot cup of mulled wine, then please get in touch at: info@thenaturalpoolcompany.com