SUMMARYWater was cultured from 39 of 48 hospitals (7 Halifax hospitals and 32 nonHalifax hospitals) in the province of Nova Scotia and from 90 residences (74 private dwellings, 16 apartments) in Halifax to determine the frequency of legionella contamination. Six of seven Halifax hospitals had Legionellaceae isolated from their potable water compared with 3 of 32 non-Halifax hospitals (P < 0 0001). Overall, 19 of 59 (32 %) of the water samples from Halifax hospitals were positive for legionellae compared with 5 of 480 (1 %) samples from nonHalifax hospitals (P < 0 0000). Five of the six positive Halifax hospitals had Legionella pneumophila serogroup 1 and 1 had L. longbeachae serogroup 2 recovered from their potable water. Legionella contamination was associated with older, larger ( . 50 beds) hospitals with total system recirculation. These hospitals also had water with a higher pH and calcium content but lower sodium, potassium, nitrate, iron and copper content.Fourteen of the 225 (6-2 %) water samples from Halifax residences were positive for legionellae -8 % (6/74) of the single family dwellings were positive, compared with 25% (4/16) apartments. The positivity rate of 15-7% for the 19 electric hotwater heaters in Halifax homes was not significantly different from the 32 % positivity for Halifax hospitals. L. longbeachae accounted for 2 of the 14 isolates of legionellae from Halifax homes.