Passengers who could be paying just 5p to fly from Leeds-Bradford International Airport to Dublin could be in for a shock if they want a drink.

Because if they buy a litre of own-brand water from no-frills airline Ryanair they will be charged almost £4 a litre.

The Dublin-based group, which made profits of £24 million last quarter, confirmed that customers are having to cough up £1.85 for a 500ml bottle of their own special brand of bottled water, Blue Rock.

A litre of mineral water costs between 80p and £1.20 but Blue Rock water has not come from a mountain stream or highland spring. It is London tap water.

The only difference is that the water has been carbonated at a plant in East London.

The water is the same as that pumped into homes all over the county by Bradford-based Yorkshire Water at a cost of less than half a penny to customers. A Yorkshire Water spokesman said: "We would always advise our customers to bottle water at its source - the tap! And to carry it with you wherever you go."

The airline would not comment further and referred all enquiries to Britvic Soft Drinks, the company that supplies the water.

The soft drinks, supplier which also makes Pepsi and Tango, created the Blue Rock Brand 18 months ago for the no-frills airline, which is one of their biggest accounts. Britvic denied the product could mislead customers and added: "We have nothing to do with the prices our customers charge their passengers." He added that Blue Rock was about to be replaced by a new product called Pennine Spring sourced from a spring in Huddersfield.

He said Britvic had acquired the company in October and had stopped production of the old product and were waiting for the sources to be depleted before supplying the new water to customers.

Earlier this month the airline was fined £24,000 after being found guilty of six breaches of the Consumer Protection Act after a judge ruled that customers were not warned about hidden costs such as taxes and fees for booking with credit cards that could add up to £30.

Ryanair, whose pilots have to buy their own uniforms, are also due to appear in court next week in a bid to discover the identity of pilots who posted comments about the airline's working practices on a website run by the British Airline Pilots' Association.