Sandwell Council has made the plea to businesses within the borough.
Legionella is a bacteria that can cause pneumonia-like and flu-like sickness, in an illness called Legionnaires’ disease.
This can be contracted by breathing in small droplets of water suspended in the air which contain Legionella bacteria. The disease is fatal in 10 per cent of cases.
Symptoms include fever, a non-productive cough and pneumonia. Legionella bacteria are naturally present in water systems.
Systems need to be regularly maintained and flushed to prevent bacterial growth that may cause illness. Warmer weather also increases the risk.
Nicola Plant, service manager for regulated services and transformation at Sandwell Council, said: "As more and more businesses prepare to reopen this summer, we are reminding them that they need to make sure their water system has been reviewed by a competent person and is safe for reopening."
The council says all water systems need to be considered.
This includes water systems at shops, hairdressers, offices, hotels, gyms, sports clubs, golf clubs, hotels, pubs, clubs, restaurants, voluntary-run premises, and anywhere that has a water supply and is currently shut.
Businesses are required by law to control Legionella and may need to approach a specialist to disinfect water systems.