Cryptosporidium can cause discomfort

However, infection expert Professor Hugh Pennington, from the University of Aberdeen, insisted there was no cause for alarm.

"Historically we have had much much bigger outbreaks than this - hundreds of thousands of people when big town water supplies got contaminated.

"By cryptosporidium standards it is not an enormous outbreak," he said.

There are normally between 500 and 1,000 cases of cryptosporidium in Scotland each year.

The infection is uncomfortable for most healthy adults, but they rarely need to be admitted to hospital for treatment.

It has an incubation period of about seven days.

Treatment plants

North of Scotland Water Authority (Noswa) is currently working with public health officials to trace the source of the infection.

Although this has not yet been established, the mains water supply is suspected.

A spokesman for Noswa said it was examining the possibility of using a process in which water could be further cleansed at treatment plants.

"The health board is saying that people can still drink the water," he added.

"The cause of the outbreak is not known - water is one of the ways that the organism is able to spread."