A total of 22 cases of cryptosporidiosis were confirmed in the Brixham area by UK Health Security Agency on Wednesday, as South West Water said it believed a damaged air valve on a pipe in a field containing cattle was a potential source of entry for parasites.
So what is cryptosporidiosis?
Cryptosporidium is a tiny organism that causes an illness in people and some animals, health officials say.
It is found in human and animal poo and can contaminate waterways, swimming pools, raw milk and fresh produce, the UKHSA says.
Anyone can get infected and there is no effective drug treatment for cryptosporidiosis, with the main symptom being prolonged diarrhoea.
Prof Paul Hunter, a specialist in microbiology and infectious disease from the University of East Anglia, says most people recover after a couple of weeks but it can be deadly for a small number of people with severely weakened immune systems.
He says most people will not need to see a doctor unless they are seriously unwell or a child.