E. coli bacteria has been detected in mains water supplies on Hobart's eastern shore, with residents in four suburbs told to boil their drinking water.
The warning for Lauderdale, Roches Beach, Acton Park and Seven Mile Beach was issued on Tuesday afternoon by state water provider TasWater.
Residents are being advised to boil water used for drinking and food preparation until further notice.
Routine sampling indicated E. coli was present in water at the Lauderdale Reservoir.
TasWater says results are not yet conclusive, but a boil water warning has been issued as a precaution while follow-up tests are undertaken.
Ice and prepared baby formula made with water prior to Tuesday's warning should be disposed of as they may not be safe to consume, TasWater advises.
Water has been supplied to a school and aged-care facility in the area.
Australian Associated Press