Thousands of people in Glasgow have been warned to continue boiling their drinking water as a row over Scottish Water's handling of an outbreak of cryptosporidium deepens.

Water bosses have denied they kept 140,000 people in the dark for more than 24 hours about the discovery of a parasite in supplies.

Scottish Water said its staff had acted "with the utmost caution" not to alarm people living in affected areas of Glasgow.

But the Scottish National Party has demanded answers from the company over the time it took to go public with the information.

The parasite can cause vomiting and diarrhoea

A Scottish Water spokeswoman said fears were raised on Friday when high levels of the parasite were found in tests taken from the supply the previous day.

GPs in Glasgow were informed on Friday to be on the lookout for a possible increase in the number of patients with problems including stomach cramps, mild flu and diarrhoea.

However, the outbreak was not made public until Saturday, when water bosses realised the parasite levels had increased further.

A Scottish Water spokeswoman said: "Issuing a public warning like this is not something we take lightly, it is a major operation.

'Fast and loose'

"We have to be absolutely sure that there is a problem before we issue a warning asking people to boil water in certain areas."

The cryptosporidium was found in water from the Mugdock Reservoir in Milngavie, East Dunbartonshire.

Those served by the reservoir were warned to boil their tap water before drinking or using it to prepare food, brush teeth or bathe babies.

Information about the outbreak has been broadcast by tannoy in the affected areas - parts of Clydebank, Glasgow city centre, Govan East, Tradeston, Plantation, Kinning Park, Hyndland, Partick, Kelvinside, Jordanhill, Drumchapel, Knightswood, Milngavie, Bearsden and Yoker.

People are being warned to boil their water

But the SNP's environment spokesman Bruce Crawford said he was concerned it had taken so long for the public to be informed.

He said: "It now seems clear that there was concern at rising levels of the parasite as early as Thursday or Friday of last week, but why then did most people only learn of it from their Sunday papers?

"If they knew and kept it from the public, then they will stand convicted of playing fast and loose with people's health."

'Remaining vigilant'

Mr Crawford said he would also be asking Scottish Water why it had been "so unprepared" for the recent floods, which are thought to be behind the outbreak.

A Scottish Water spokeswoman said a joint incident team was reviewing test results so the boil instruction can be lifted quickly.

Dr Jim McMenamin, chairman of the team, said people were being urged to boil water purely as a precautionary measure.

He added: "I am encouraged that we have not seen any cases of diarrhoea attributable to this incident. We are, however, remaining vigilant."

Bottled water sales have soared

First Minister Jack McConnell has asked for a report on the problem from environment minister Ross Finnie and health minister Malcolm Chisholm.

The problems have triggered a sharp rise in demand for bottled water at supermarkets.

Sales of bottled water at Asda stores at Govan on the south side of Glasgow and Bearsden in the west end of the city have soared.

Safeway also described its bottled water sales as "phenomenal".

A normal week's order sold out in one day at its Knightswood store and emergency supplies were ordered for stores in Partick and Byres Road.

Scottish Water has set up a helpline on 0845 600 88 55. Anyone concerned about their health should contact NHS Scotland on 0800 22 44 88.