Northern Ireland Water Board officials believe they have traced a section of piping which might have led to the contamination of water supplies in the greater Belfast and Lisburn areas with the cryptosporidium bug.
The bug can cause severe diarrhoea, nausea and stomach cramps and particularly affects children and the elderly. So far there have been 76 confirmed cases of people who have contracted it.
The Department of Regional Development yesterday confirmed that up to 100,000 people in around 28,000 households remained at risk.
People in affected areas are still advised to boil all their drinking water. It is believed that sheep and cattle droppings were washed into reservoirs by recent heavy rain, thus causing the outbreak.
The Minister of Education, Mr Martin McGuinness, announced that about 50 schools in the affected areas would be supplied with bottled water immediately and that the department would meet the costs.
