Residents have been urged by Anglian Water to boil all their water until further notice to protect them from a bacteria called cryptosporidium found in water supplies which can cause severe stomach upsets and can pose a serious health risk to the very young and elderly.
The problem, which affects 250,000 people, could take weeks to resolve.
Areas at risk include Old, Walgrave, Sywell, Hannington, Holcot, Scaldwell, Pitsford, Brixworth, parts of Northampton and Daventry.
It has also been reported Pitsford Reservoir could the source of the bug.
A spokesman for Anglian Water said: "This is being taken very seriously as it could lead to real health problems for the very young and elderly.
"We apologise for the inconvenience this will cause."
The bacteria was found during routine tests of the water supply.
Last year, there was a similar problem in Norfolk, following flooding that took 10 days to resolve.
Chrissie Osborne, who lives near Hannington and has livestock, is among those affected.
She said: "I wasn't aware of this and have just drank some water with a
tablet.
"I'm not a great water drinker but I know lots of young people drink water these days so I'm afraid they might be at greater risk.
"I fill the water up for my hens but the rest of my animals drink from the water which collects in their troughs so hopefully they will be alright. I want to know if something could have been done to avoid this problem or whether it has been caused through mismanagement of the water."
The advice to boil water applies to any tap water which is used for drinking, cooking, cleaning teeth or for pets, but customers have been reassured tap water remains safe for washing, bathing and toilet flushing.
Alternative water supplies are currently being investigated for the affected areas, but due to the size of the area affected bottled water will only be delivered to special needs customers on Anglian Water's WaterCare register.
For further information visit
www.anglianwater.co.uk. Anyone who is worried about their health should contact their doctor or NHS Direct on 0845 4647.
Click here to read about the bottled water shortage.
Click here to read more about the closure of schools.
Click here to read more about Cryptosporidium.Click here to read more about how pets could be affected.Click here to read a Cryptosporidium Q and A.Click here to read a police warning.If you affected by the crisis sign-in by clicking the blue Register button or post your comments to here.The following areas have been affected: Collingtree
Grange Park
Great Houghton
Hardingstone
Northampton -castle
Northampton -delapre
Northampton - kingsley
Northampton Kingsthorpe
Northampton St Crispin
Northampton St James
Northampton - Weston
Wootton
Northampton billing
Northampton eastfield
Northampton ecton brook
Northampton headlands
Northampton lumbertubs
Northampton thorplands
Northmpton weston
Great Houghton
Northampton abbington
Northampton Boughton green
Northampton castle
Northampton eastfield
Northampton headlands
Northampton Kingsley
Northampton Kingsthorpe
Nothamtpon Parklands
Northampton St Crispin
Northampon St David
Northampton Thorplands
Northampton weston
Boughton
Brixworth
Chapel Brampton
church brampton
cottisbrook
hannington
harleston
holcot
moulton
northampton boughton green
northampton st david
old
Overstone
Pitsford
scaldwell
sywell
walgrave
Ashby St Ledger
Badby
Braunston
Bugbrroke
Byfield
Canons Ashby
Catsby
Charwelton
Collingtree`
Daventry
Dodford
Everdon
Fatheringstone
Fawsby
Flore
Grange Park
Harpole
Hellidon
Kislingbury
Milton Malsor
Nether Heyford
Newnham
Norton
Preston Capes
Rothersthorpe
Staverton
Stowe Nine churches
Upper Heyford
Upton
Weedon Bec
Welton
Woodford cum membris
Duston
Northampton Kingsthorpe
Northampton Spencer
Northampton st james
Upton
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