Residents in an inner Hobart suburb may have to keep boiling their water for several days after the state's water authority found E. coli during routine sampling.
Bacteria was discovered in the South Hobart water supply on Tuesday but the boil water alert for the suburb wasn't issued by TasWater until Wednesday night.
Department manager Lance Stapleton said on Thursday the company had fixed the problem but water wasn't yet safe to drink.
Around 1000 properties have been affected.
"We're anticipating the alert will be lifted some time over the weekend," Mr Stapleton said.
A South Hobart child care centre owner said she received a letter from TasWater on Anzac Day and has since bought heaps of bottled water for drinking and washing food.
"We're taking all precautions," Child Play's Early Learning director Mirela Djukanovic told AAP.
"We were certainly surprised, we haven't had anything like this before."
It is the second time in six months a Hobart suburb has been told to boil their water after Risdon Vale residents were issued the same alert in November.
Mr Stapleton said the most recent problem was caused by non-chlorinated water mixing with the treated water supply.
"We're not talking raw sewage. We're talking water that was not sufficiently chlorinated to get rid of all the bacteria," he said, adding the problem had been isolated.
"We need to keep moving good water through the system and keep testing."
Drinking the contaminated water could cause diarrhoea and vomiting.
