The utility company has announced costs will go up by 2.8% in April, meaning the average water charge for households across Scotland in 2013/14 will be £334.

Water charges have been held since 2009, and the increase is below the rate of inflation. The rise has been agreed with the regulator, the Water Industry Commission for Scotland.

Douglas Millican, interim chief executive, said Scottish Water is investing £2.5 billion in infrastructure, and the price rise was a fair deal for customers.

He said: "The quality of our drinking water is the best it has ever been, we are continuing to improve the natural environment across Scotland, cutting water leaking from our pipes and customer service is continuing to improve."

However, Trisha McAuley, senior director at Consumer Focus, said: "It is a particularly tough time for consumers. Many are struggling to balance household budgets with food and utility bill price hikes and while this is Scottish Water's first price increase in four years, it is nevertheless unfortunate."

Tory infrastructure spokesman Alex Johnstone said: "This will be noticed on household bills across Scotland.

"While this rise still compares favourably with water charges south of the Border, what this figure does not take into account is the fact Scottish Water is also given significant sums of money by the Scottish Government.

"So, as well as the household bill, you have to factor in people's taxes which would give you a higher figure than the £334 quoted."

Labour MSP Richard Baker said the increase came "on the heels of gas and electricity price rises, making it even more difficult for hard-working families to make ends meet".

He said: "There is a strong argument this increase has come in response to the SNP cutting the budget for Scottish Water.

"Each small increase in costs combines to create a real and painful squeeze for families, which makes for an unhappy start to 2013 for tens of thousands of Scots."