HOLIDAY accommodation with a swimming pool is often one of the most important things to Brits booking a trip away.
What you may not realise, however, is that the pool could be hiding a number of deadly bacteria – even if the water looks completely clean.
Getty – Contributor A clear swimming pool may not mean it is still clean
Luke Griffiths, qualification development manager at Safety Training Awards, told Sun Online Travel what to look out for before getting into a swimming pool.
He said: "Just because pool water looks clean and clear it may still harbour harmful micro-organisms such as Cryptosporidium, so try not to drink the pool water."
Luke revealed that two nasty parasites that cannot be seen with the naked eye are Cryptosporidium and Giardia.
The Cryptosporidium parasite is one of the most common causes of stomach infections and can result in cryptosporidiosis, which leads to diarrhoea, nausea, fever and stomach pain.
Alamy Cryptosporidium is the leading cause of gastrointestinal illnesses
Alamy Giardia is also a common parasite which can cause stomach problems and diarrhoea
While most healthy people can recover within three weeks, anyone with a weak immune system could face other life-threatening symptoms.
Last year, a 12-year-old girl was hospitalised after contracting cryptosporidium while swimming on a beach.
And Sun Online had previously reported how dozens of British holidaymakers were left with crippling diarrhoea after a suspected outbreak of the bug at a hotel in Tenerife.
There is no specific treatment for the bug according to the NHS, but sufferers are advised to take plenty of fluids and re-hydrate.
How diarrhoea illness Cryptosporidium or Cryptosporidiosis is caused and how it's sometimes found in swimming pools
Another common stomach bug is Giardia which is highly infectious.
Symptoms include smelly diarrhoea, tummy pains or cramps, bloating and farting.
The bug can be treated with antibiotics, and usually clears up in a week, but you will need to have your stool tested first.
Luke also warned: "Be mindful that cloudy looking water can indicate problems with the pool and the water may contain harmful micro-organisms or dangerous chemical properties."
Alamy Pseudomonas aeruginosa can also be found in dirty swimming pools
Getty – Contributor Parents who are concerned can ask their hotel to conduct a test of the water for bacteria
You should stay out of the pool if "the clarity of the pool is so poor that you can’t see the bottom".
Other common signs of a dirty pool include a "slimy coloured growth on pool walls, floors and tiling [which] could indicate algae or other biofilm growth".
He added: "This could harbour unhealthy micro-organisms such as Pseudomonas aeruginosa."
The science behind why you shouldn't be peeing in the swimming pool
Pseudomonas aeruginosa could lead to serious problems for someone already unwell.
The type of illnesses triggered by the bug depends on how it enters the body, but can range from pneumonia to septic shock.
Brits who are concerned about the safety of the swimming pool can ask their hotel to do a chemical and microbiological test of the water to check for bacteria, or they can test it using their own strips which can be bought online.
To check if a specific hotel is deemed safe, Check Safety First list the resorts around the world which have passed their inspections.
Sun Online Travel previously reported how the smell of chlorine could mean a swimming pool is unclean, contrary to popular belief.
And last year, a family's "holiday from hell" saw their young children swimming in a pool which had poo in it during a £1,500 trip to Tunisia.
They were forced to leave the hotel just hours after arriving due to the condition of their rooms.