According to the CDC, it takes less than a minute for E. coli to be inactivated if chlorine levels are adequate, about 16 minutes to control Hepatitis A virus, about 45 minutes to kill off the Giardia parasite and over 10 days for a Crypto parasite.

CNN: Yuck! What's in your pool water

The report said the hospital had made an "investment in measures to control legionella" including the introduction of a silver and copper ionisation disinfection system, to replace its chlorine dioxide one.

BBC: 'Legionella concerns' remain at Basildon hospital