Thousands of residents must continue to boil their tap water before drinking it following a parasite outbreak in Devon.

South West Water (SWW) said it would not lift the “boil water” notice in place for around 2,500 homes in Brixham “until we and our public health partners are completely satisfied it is safe to do so”.

About 17,000 households and businesses in the area, supplied by SWW, had been told not to use their tap water for drinking without boiling and cooling it first.

It came after confirmed cases of cryptosporidium – a waterborne disease which can cause unpleasant symptoms such as diarrhoea and vomiting – began rising in the fishing town.

The UK Health Security Agency (UKHSA) said on Friday this number had reached 46.

David Harris, incident director at South West Water, said: “Our teams on the ground continue to work as quickly as we can to resolve the situation in the Hillhead supply area, where we are still advising around 2,500 properties to boil their drinking water before consuming.

“We are urgently investigating the damaged air valve on private land which we believe to be the probable cause, and following the draining and cleaning of Hillhead reservoir we have now refilled the largest of the two tanks within the reservoir and we have isolated the second tank.

“We are working 24 hours a day, and early this morning we commenced flushing of the wider Hillhead network as we work to eliminate any traces of cryptosporidium.

“We will not lift the boil water notice in Hillhead until we and our public health partners are completely satisfied it is safe to do so.”

The microscopic parasite which caused the waterborne disease likely entered the water network through a damaged air pipe in a field containing cattle, the company previously said.

The number of confirmed cases is expected to continue rising for up to two more weeks because of a delay in symptom development caused by the parasite’s incubation period.

SWW said an additional £100 compensation will be paid to customers in the areas which continue to be affected – bringing the total to £215.

Business owners in Brixham have complained about the lack of contact from SWW.

Sally Dart, who runs homewares shop Flotsam 50 near Brixham Harbour, told the PA news agency that business was “probably 30 to 40% down” and described the water company as “appalling”.

Ms Dart said locals first felt symptoms after a busy, pirate festival held in the town between May 4 and 6.

Referring to SWW, she added: “They knew they had this problem – obviously the reservoir couldn’t cope for some reason or another, it was getting all the stuff off the field into it.

“No one was checking the quality of the water and we’ve all got sick and it’s stupid, really.”

Three stations continue to offer safe bottled water to customers alongside direct deliveries to vulnerable customers, schools, hospitals and care homes.

Conservative MP Anthony Mangnall, whose Totnes constituency includes Brixham, had previously told PA that SWW’s response to the outbreak was “contemptible and just generally incompetent”.

The company said affected residents can continue to use their tap water as normal for washing, bathing and flushing the toilet.

The disease can be picked up directly from the faeces of another person or animal, from swimming in or drinking contaminated water, or by eating contaminated food such as unwashed vegetables.