Millions of potentially harmful types of bacteria have been found in holy water, which are being passed between people at mass, according to a young scientist from Donegal.

14-year-old Conor Farrell from St Eunan’s College in Letterkenny is one of 550 projects in the BT Young Scientist and Technology Exhibition, which opens today in the RDS in Dublin.

12,000 students are involved in projects ranging from how to catch a sheep, making the perfect cup of tea and whether a bike with two chains will go faster.

Conor Farrell says he tested holy water in churches and found that harmful bacteria was being passed from person to person.

But he found a small amount of bleach in the water can stop it.