More than 100,000 households have been affected and a total of 19 schools across the area closed on Wednesday amid fears supplies of bottled water would not last the day.
There were also angry scenes in supermarkets as shoppers battled to get the last few bottles of water available.
The panic buying was sparked after Anglian Water announced traces of cryptosporidium, which can cause sever diarrhoea, were found in water supplies.
Anglian Water has said it is investigating the cause of the problem and asked all residents only to use boiled or bottled water.
List of schools closed on Thursday - click hereA spokesman for the firm said: "Until further notice, Anglian Water customers in Northampton, Daventry and west of Daventry areas are being instructed to boil their drinking water before using it.
"Only once drinking water has been boiled and allowed to cool should it be used for drinking, preparing food or cleaning teeth. This advice also applies to pets.
"Tap water remains quite safe for washing, bathing and toilet flushing.
"Anglian Water has taken this precautionary measure while it investigates routine samples that have shown evidence of cryptosporidium in the water supply.
"The company apologises for the inconvenience this will cause, but stresses that the health and safety of its customers must come first."
During a day of water problems on Wednesday, nursing home staff were told to boil water before using it for washing vegetables or letting residents drink it.
Vets also stocked up on bottled water following advice that tap water was not safe for animals to drink.
Restaurants and pubs also suspended the sale of soft drinks made with tap water and a least nine supermarkets were reported to have temporarily sold out of bottled water.
Anyone who is worried about their health should call their doctor or call NHS Direct on 0845 4647.
Click on the links below for more stories on the tap water alert:
ThursdayFamilies told to boil water by mistake - click hereAnglian Water information unti breaks down on way to Northampton - click hereCrisis 'may take weeks to resolve' - click hereWorst water scare ever in region - click hereAnglia Water information unit in town centre today - click hereWednesdayUrgent warning to Northampton and Daventry residents to boil waterSchools in Northamptronshire close after water alertFull list of affected areas in Northampton after water supply warningSymptoms can last for weeksNorthamptonshire schools advised to close following water contaminationDistraction burglary advice following water problemsResidents urged to be vigilant over hygieneUrgent appeal for water for dogsSupermarkets in Daventry run dry after panic buyingMPs call for government investigationBarclaycard gives free bottled water to staffAnglian water will deliver to schoolsThe full article contains 489 words and appears in n/a newspaper.
