The Canterbury District Health Board says it has received 110 gastroenteritis notifications from the Darfield Medical Centre.
Canterbury Medical Officer of Health Dr Alistair Humphrey says 10 of the notifications have already been confirmed as campylobacter, but other organisms may also be identified.
He says the gastroenteritis outbreak is likely to result from problems last week with Darfield and Selwyn Rural water supplies.
He says the Selwyn District Council has since corrected the issue with its deep underground bore system, and water supplies are safe to drink.
Dr Humphrey says gastroenteritis can easily spread and people with the illness need to rest and keep well hydrated.