​Managing the risks of hot tubs and play pools

With the promise of warmer weather just around the corner, the British public will be heading into their gardens in droves, uncovering their hot tubs, digging out their kids’ paddling pools and untangling their hoses, ready for the summer sun. However, many people will be oblivious to the hazards that can impact them and their families, so it’s important that installers educate them on how to safely enjoy their pools and hot tubs.

Risky business

The combination of the initial lockdown and an unusually warm May in 2020 saw a huge increase in purchases of hot tubs, with sales on eBay rising by 1,080%.

Although hot tubs and pools are built for fun there are serious hazards such as backflow, scalding and the risk of legionella that people need to be made aware of.

“Sales of hot tubs soared during the first lockdown, but so did the risks,” says Jerry Whiteley, CIPHE technical manager. “And legionella cases were already on the increase before this.”

Legionnaires’ disease is a type of pneumonia, caused by the legionella pneumophila bacterium found in warm water environments such as hot tubs. Legionnaires’ disease can be fatal but, if detected early, it can be treated. Symptoms include loss of energy, high fever, dry cough, aching muscles, headache, chest pains and shortness of breath. Anyone with suspected Legionnaires’ disease must seek medical help immediately.

Keep it clean

When it comes to hot tubs it’s vital that the water they contain is clear, clean and hygienically safe. To achieve this consumers need to treat the water to BISHTA Standards with disinfectants, oxidisers, minerals and pH balancers.

Testing water to ensure it is safe and hygienic is important. Consumers can easily test water with an inexpensive kit to determine the pH and sanitiser levels, and make any adjustments required. Test strips and tablets have use-by dates, which are important to follow.

The British and Irish Spa and Hot Tub Association (BISHTA) recommends the continuous use of a residual sanitiser –a substance that rapidly kills potentially harmful micro-organisms and leaves a residue in the water, which can be measured. A residual sanitiser must be used, irrespective of any other back-up equipment or substance, such as an ozone generator or mineral cartridge.

“Sanitiser kills bacteria and viruses that could be potentially harmful to bathers if left to multiply unchecked in warm water,” explains Chris Hayes, managing director of BISHTA and SPATA (the Swimming Pool and Allied Trades Association). “Hot tubs are small bodies of water with relatively high bathing loads. As water is used and recirculated, water treatment products and other particulates that aren’t removed by the filters build up over time, and there comes the point when even if correct water maintenance regimes are applied, the water looks and feels lank and lifeless, and the only corrective action remaining is to drain the hot tub down and refill.”

BISHTA recommends that water should be changed a minimum of every month and an absolute maximum of three months to maintain water quality. However, specific HSE guidelines apply to hot tubs in holiday lets and other business settings that require more regular draining and refilling.

Optimising efficiency

With the cost of living rising at an alarming rate, many consumers who invested in a hot tub over the last couple of years will be looking for ways to cut down on running costs as energy tariffs rise.

Size matters and influences the running costs because the bigger the hot tub, the more expensive it will be to run as there’s more water to heat. While the average hot tub holds around 1,000 litres, swim spas contain in excess of 10,000 litres.

Water temperatures are typically set between 36°C and 40°C, but during hot weather this is often reduced. The higher the temperature, the more energy needed to maintain it and the more it will cost.

“When the cover is off, the ambient air temperature will also have a bearing,” says Hayes. “The greater the difference between the water temperature and the air temperature, the more rapidly heat is lost. Obviously, the more the hot tub is used – when the cover is off, and the pumps (and blowers, where fitted) are running – the more it will cost to run as, not only do you have to factor in electricity required to drive a pump or blower, but an agitated, aerated water surface will lose heat faster than calm water.”

In the experience of BISHTA members, typical costs can range between £1 and £2 per day (for an average use of a half-hour per day) for a quality hot tub from a reputable manufacturer. However, with energy price increases this is likely to cost considerably more.

“Water treatment chemicals are other costs associated with owning and running a hot tub,” adds Hayes. “Chemicals are a vital requirement in ensuring that hot tub water is kept clear, clean and hygienic. Allowing an annual budget of approximately £300 should cover water treatment chemical requirements, though more frequently used hot tubs and swim spas may require a bigger budget.”

Water waste

Although many consumers are now more mindful of their water consumption, this precious resource can still be wasted, particularly when using hot tubs and temporary pools.

“We are facing water shortages now and in the very near future we can expect to see big changes coming our way with our usage, designing systems and installing products that

will all be energy saving and conserving water,” predicts Whiteley.

“Using leisure products, that might be deemed wasteful by some, may soon become even more of a luxury item than when first purchased.”

If anything will encourage consumers to curb their consumption of water it’s the cost. According to Water UK, water bills will rise by almost 2% in England and Wales this year, which could see the use of hot tubs and temporary pools drop.

Danger zone

According to the CIPHE, there has been an increase in people filling play pools and hot tubs with hot water directly from the dwelling’s hot water system, which greatly increases the risk of burns and scalds.

A CIPHE member actually witnessed a householder filling a pool with hot water directly from the hot tap, via a hose pipe, with no cold water blended or backflow prevention.

“Hot water is category 2 because it has been heated,” explains Whiteley, “However when discharged into a swimming pool or hot tub the category changes again as the equipment is filled because there might be chemicals added. It can even become as high as category 5, depending on the circumstances of use.

“What is also a grave concern is the hot water filling this pool or hot tub might be at a temperature of 55°C. This was the case at the previously mentioned incident with no one watching over the filling. Leaving a leisure pool or hot tub unattended whilst filling directly from a hot water system is just an accident waiting to happen.”


When filling hot tubs or pools, backflow prevention must be considered, but generally it isn’t something that people are aware of. It’s a good idea for installers to speak to their customers about the risks to ensure that they have the right devices in place to prevent backflow occurring when filling their pools and hot tubs.

“Hot tubs are generally sited in the same place each time they are used; therefore, a suitable thermostatic tap and backflow device should be applied,” says Whiteley. “Of course, the water is mostly heated using electricity for hot tubs at great expense, but some people are adding the home system to speed up the process.”

Due to the possibility of contamination, particularly with faecal matter, the water in a spa pool or hot tub is categorised as fluid category 5 – the highest level of risk to public health, should the fluid contaminate drinking water.

“The Regulations and Bylaws specify that the water supply upstream of a spa pool or hot tub must be protected against backflow by installing a recognised fluid category 5 backflow prevention arrangement, such as an AA or AB air gap,” explains Hayes. “Maintaining a suitable air gap between the water already in the spa pool or hot tub and water being added will ensure that there is no possibility of back siphonage, which could contaminate the drinking water supplies in the mains water system.

“Water suppliers have agreed, through the WRAS Technical Committee, that it is acceptable for a spa pool or hot tub, used only by the occupants of a single privately owned or rented domestic property, to be topped up using a hand-held hosepipe supplied from a hose union tap protected by a double check valve (fluid category). This is providing that the hose is fitted with a self-closing trigger mechanism; the hose is not immersed in the spa pool or hot tub, drains or any other fluid, and a clear air gap is maintained at all times between the end of the hose pipe and the water in the hot tub being filled.”

Useful resources

BISHTA is the UK’s independent trade association for the hot tub industry, setting the industry standards and promoting high standards of safety and enjoyment by registering suppliers of spas, hot tubs, accessories, and water purification products.

Check the BISHTA website for details of their member companies and use their easy postcode search map to find members close by.


The Health Protection Agencies, including Health Protection England and the Health and Safety Executive, recognise and consider the use of oxidising biocides essential for the control of legionella and other infectious agents in spa-pool systems, such as chlorine, bromine or PHMB (Biguanide). For more information, visit www.hse.gov.uk/pubns/books/hsg...

Find out more

To find out more about the risks, download HSE’s guide – The control of legionella and other infectious agents in spa-pool system – which can be found at www.hse.gov.uk/pubns/books/hsg...

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