It has been talked about for years and now the sugar tax is finally here.

Water and juice-based drinks containing more than five grammes of sugar per 100ml are now liable for the Sugar Sweetened Drinks Tax.

Drinks containing between five and eight grammes of sugar will cost an additional 20c per litre.

If there is more than eight grammes, the tax will be 30c per litre.

Drinks that will be affected include some flavoured waters, carbonated waters, energy and sport drinks, and juice-based drinks.

Some concentrated products that require the addition of water before consumption such as cordials, bottled squashes and flavoured syrups are also liable for the tax.

Pure fruit juices will not cost more, unless sugar is added, pushing the entire sugar content above the threshold.

Brands such as Coca-Cola Classic, Pepsi, Club Orange, Red Bull and Monster will all cost more, although diet and low sugar versions will be unaffected.

Dairy products are outside the scope of the tax on the basis of the nutritional value they offer, such as calcium and protein which are necessary for good health.

The Irish Heart Foundation, which campaigned for the new tax, said that today was the most significant day yet in the fight against childhood obesity in Ireland.

The foundation's head of advocacy Chris Macey said the measure was the first signal that the Government was prepared to take tough action to tackle the crisis and the decision had already paid off due to a major programme of reformulation by manufacturers to reduce sugar levels below the thresholds chosen for the tax.

While the primary aim of the new tax is to help tackle obesity levels across society, it will also raise some revenue for the State.

How much that will amount to remains the subject of debate, however.

The Department of Finance, Public Expenditure and Reform estimates it will raise €40 million in a full year, but as drinks manufacturers work to reduce sugar content the figure will fall.

The Irish Beverage Council, which represents soft drinks companies, opposed the introduction of the tax, but has accepted that it is now a reality.

The council claims that 76% of soft drinks sold in Ireland will not be liable for the tax as companies have been working to reduce sugar for more than 30 years.

Colm Jordan of the IBC said 10 billion calories have been removed annually between 2005 and 2012 through voluntary sugar reduction in soft drinks.

He said that amounts to a 10% reduction in seven years, and that soft drinks represent less than 3% of Ireland’s calorific intake.

The tax will operate in the style of excise duty and 'first suppliers' of taxable drinks will be liable to collect and pay the tax to the Revenue Commissioners.

First suppliers are defined as those who import or manufacture such drinks and sell them on to wholesalers, retailers or consumers.

The first indication of the actual amount the sugar tax will raise will come at the end of July, the deadline for suppliers to return their first two months of collected sugar tax.

The Chairman of the Royal College of Physicians of Ireland Policy Group on Obesity has said the sugar tax is the first solid, concrete step the Government has taken to tackle the obesity epidemic, adding it is the single measure 'most likely to work.'

Professor Donal O'Shea, a consultant endocrinologist, told RTÉ's Morning Ireland that 20,000-40,000 people have died from obesity-related conditions over the last ten years.

He said the tax is already working because the drinks industry has already taken steps to reduce sugar in drinks.

However Mike Gibney, Emeritus Professor of Food and Health in UCD, pointed out that a salt reduction programme, running since 2004, has resulted in a massive reduction in salt in a number of foods including bread and breakfast cereals.

Speaking on the same programme he said this had been achieved without taxation.