A 59-year-old man with hypertension and hyperlipidemia, who was a smoker and fond of gardening, was admitted to our hospital because of fever and dyspnea. A chest radiograph revealed bilateral pulmonary infiltration and pleural effusions. He was diagnosed with Legionella pneumonia because a urine sample was positive for the Legionella antigen. He was treated with intravenous pazufloxacin and oral rifampicin, as well as controlled mechanical ventilation. Despite these treatments, the bilateral infiltration (as assessed using chest radiography) worsened. Allowing for heart failure and acute respiratory distress syndrome (ARDS), he was treated with intravenous furosemide and pulse methylprednisolone. A few days later his respiratory failure recovered, and he was discharged. Serogroup 1 was isolated from his sputum, as well as from his private garden hose and the water contained within it. Both samples exhibited the same pathogen, as assessed by genetic analysis using pulsed-field gel electrophoresis (PFGE). This is the first case of L. pneumophila pneumonia caused by a private garden hose and confirmed by genetic analysis. The present study showed that a private garden hose should be considered as a cause of Legionella pneumonia.