Swimming Pool Temperatures

PWTAG are often asked what temperature the pool water should be; what is too hot, what is too cold?
There are no regulations on what temperature swimming pool water should be and whilst PWTAG try to effect what temperatures are used it is decision that is left to the discretion of the pool operator.

PWTAG have tried to influence this situation to help provide the best conditions for swimmers and working together with our partners have produced the following guidance which is in our text book Swimming Pool Water and in our Code of Practice which tends to be used by the swimming pool industry as the standard to follow.

Pool Water Temperatures

The temperature of swimming pool water is frequently an issue with swimmers and equally the temperature and atmosphere in the pool hall is an issue for swimming teachers, coaches and lifeguards. Unfortunately, there is no common ground as the complaints range from being too cold to too hot and it is clear that every swimmers preference cannot be accommodated at the same time.

Pool Managers have a general perception that is supported by empirical evidence that the warmer the pool water the more swimmers wish to use the facility. Hence over many years the pool water temperature has tended to creep upwards. Public demand aside there are very good reasons for controlling the pool and air temperatures in a pool hall to within a range of temperatures that provides comfortable bathing without causing undue risk to the swimmers.

Obviously the temperature range that the human body can withstand is very wide, which is why individual preferences can vary so much; Some pools do need to be warm – e.g. for parents and toddlers. But operators tempted to join the move towards higher temperatures should bear in mind that they do create a number of problems.

  • Microorganisms multiply faster – up to twice as fast for a rise of 10 degrees C; filters are increasingly likely to become colonised.
  • Bathers get hotter – limiting serious swimming and increasing sweat and grease in the water.
  • Energy costs, direct and indirect, are higher – whatever efficiency or conservation methods are used.
  • Air temperatures, which are linked to those of the water, rise too – making the atmosphere less comfortable for staff and others (as can the higher moisture levels).
  • There is more moisture in the pool atmosphere, even when relative humidity is controlled at the same level – with a risk of condensation and possibly corrosion and deterioration of the building and equipment.
  • Dissolved gases become less soluble – releasing worse smells (chloramines) and potentially harmful trihalomethanes; and pH value rises as carbon dioxide escapes.

With an increasingly wide variety of pool uses, and operators attempting to introduce more flexibility into programming of pool operation, it is obviously difficult to select a single appropriate or optimum operating temperature for any particular pool. The large volumes of water involved make it impossible to vary water temperatures rapidly in any one water area. This means that careful selection and accurate control of the optimum water temperature for each pool is essential.

Pool hall air temperature

The temperature of the pool hall air should normally be maintained at the water temperature – or no more than 1 degree C above or below. But it is recommended that air temperatures over 30°C should generally be avoided for reasons of energy economy. Clearly there may have to be compromises where, for example, mothers and toddlers have to be accommodated in the same area as fitness swimming. There are two good reasons to maintain the air temperature within this range.

1. To ensure that there is no excessive evaporation of the pool water into the atmosphere causing wasted heat loss and an uncomfortable increase in relative humidity.

2. If the pool air is lower than the pool water temperature when a swimmer exits the pool the water on the swimmers skin evaporates into the atmosphere causing a cooling effect on the skin, which makes the swimmer feel cold regardless of high pool water temperatures.

Therefore to achieve a pleasant bather experience it is more important to have a balanced air/water temperature than have really high water temperatures.

For these reasons the industry has attempted to self-regulate and the Pool Water Technical Advisory Group (PWTAG) supported by its member organisations including the Amateur Swimming Association has published a guideline of recommended maximum pool water temperatures for specific swimming activities.

The chart here gives PWTAG’s recommendations on water temperatures for different types of pool and activity. They are the recommended temperatures ranges and operators are required to select the appropriate temperature for their particular pool and activity.

Pool temperature image

Swimming Teachers, Coaches and Lifeguards

Swim England say that given that the pool air temperature is inevitably going to be above 28°C and possibly as high as 33°C the working conditions on the pool side are going to be uncomfortable even oppressive. Clearly such a temperature range is well outside the norm for workers as identified in health and safety guidance and regulations, and for that reason Swimming Teachers, Coaches and Lifeguards should clearly be considered in that group of workers identified in the Working Time Regulations as requiring more frequent breaks from such a harsh working environment.


Guidance from PWTAG, HSE, Sport England, BSI and European Standards say that in terms of safety bather loading then the formula to start from is 3m2 per bather. It is just a starting point on which to base a figure on and should be varied to take in to account other safety factors like for example the type of use and the type of user.

PWTAG then go on to say that when designing or operating the pool, this figure should also reflect the loading that the pool plant has been designed to accommodate. This should consider that there are likely to be more bathers in shallow water than in deep water areas where swimming is required. Hence the formulae in areas less than 1 m depth is 2.2 bathers per m2, in areas of 1 to 1.5 m depth is 2.7 bathers per m2 and in areas of water deeper than 1.5m is 4 bathers per m2.

Shallow water pool
In a shallow water pool, for example, 10m by 10m = 100 m2 @ 3m2 per person = 33 people max safety design load.

If this was a pool < 1m depth, then the pool plant should be designed to accommodate 45 people - the instantaneous bathing load (2.2 people per m2).

To calculate the turnover (the time taken for the total contents of the pool to be circulated through the treatment plant to filter and disinfect the water):

The circulation rate is then 45 x 1.7 = 76m3h
The turnover period is then water volume divided by circulation rate =
100m3 ÷ 76m3h = 1.3 hrs

Or, preferably, from the turnover table in Swimming Pool Water, the turnover period for the pool would need to be 30 to 75 minutes.

If this was the case, then at times, say a children’s play session or an aerobic session, the normal loading in terms of the pool water quality could be increased to 45 always providing that physical safety factors are taken in to account also.

Deep water pool
If this was a deep pool 10m by 10m = 100 m2 = @ 3m2 per person = 33 people max safety design load.

If this pool was 2m depth throughout then the pool plant should be designed to accommodate 25 people (4 people per m2).

To calculate the turnover:
The circulation rate is 25 x 1.7 = 42
Turnover period is then water volume divided by circulation rate = 200 divided by 42 = 4.76

Or, preferably, from the turnover table, the turnover period for the pool would need to be 4 hours.

In this case, the pool bather loading should always be restricted to 25 persons as this is the capacity of the pool water plant.