It was lifted three days later, on March 15, but restored on March 17.
That warning was eventually lifted on Sunday, when CDC said workers had found the faulty equipment responsible for the results.
However, another positive result was reported at 1pm on Thursday, at CDC's Fisher Pl testing site.
Dave Gittings, CDC's infrastructure, services, and regulatory manager, said he was "extremely disappointed and surprised" to receive the report.
"We do appreciate how frustrating this will be for our residents over the long weekend.
"We have alerted the district health board and the local medical centre as a precaution and we are taking all steps necessary to keep our community safe.
"We urge people to follow the boil water instructions and to check on your neighbours and older family members."
Water experts Lutra, which also dealt with Martinborough's 2019 outbreaks, have been called in again.
Jason Colton, Lutra's chief executive, said the council had eliminated a number of potential contamination sources and has located and fixed two probable contamination sources.
"This latest positive result shows that there is at least one other potential contamination source in the water supply network that needs to be located and rectified.
"This is proving challenging to locate."
Water is available from outside the Carterton Event Centre.
Advice for residents
The risk of getting sick from drinking the water is low but possible, especially for vulnerable people. Babies, young children, pregnant women, the elderly and people who have weakened immune systems are more at risk of illness. If you get diarrhoea, vomiting and/or a fever, get advice from your doctor or contact Healthline on 0800 611 116.
How to boil water for drinking:
• Boiling will kill all disease-causing organisms
• Bring water to a rolling boil (where bubbles appear in the centre and do not disappear when the water is stirred) for one minute or boil a full electric jug until it switches off
• Cool water (do not use ice cubes to do this) and pour into a clean container with a lid
• Refrigerate until needed
• If you experience diarrhoea, vomiting and/or a fever, contact your doctor or Healthline on 0800 611 116
For more information and to stay up to date, visit cdc.govt.nz/boilwaternotice