According to the World Wildlife Fund, water used for livestock production is expected to rise by 50 per cent by 2025 and at present it accounts for 15 per cent of all irrigated water.

The global average water footprint of beef is 15,400 litres per kilo, which is predominantly green water – water from renewable sources - (94 per cent).

The water footprint related to animal feed takes the largest share with 99 per cent of the total, while drinking and service water contribute just one per cent to the total water footprint.

However, drinking water is 30 per cent of the blue water footprint.

The major part of the water footprint of a beef cow, 83 per cent, is attributed to beef, but smaller fractions go to the other products such as offal, leather and semen.

However, analysts say that one piece of beef can be very different from another and the precise water footprint of beef depends on the production system - grazing, mixed or industrial - the composition of the feed and the origin of the feed.

Beef from industrial systems generally has a lower total water footprint than beef from mixed or grazing systems because of the better feed conversion rate.

However, the concentrates in cattle feed and their water footprint means that beef from industrial systems has generally larger blue and grey water footprints than beef from mixed or grazing systems.

The water footprint of meat from beef cattle at 15,400 litre/kg on average globally is much larger than the footprints of meat from sheep (10,400 litre/kg), pigs (6,000 litre/kg), goats (5,500 litre/kg) or chickens (4,300 litre/kg).

Animal products generally have a larger water footprint than crop products.

According to studies by Mekonnen and Hoekstra (2010, 2012), the global water footprint of beef production between 1996 and 2005 was about 800 billion cubic metres per year.

The global average water footprint of milk is 1,020 litre/kg and the water footprint of cheese is 5,060 litre/kg. For eggs the water footprint is 3300 litre/kg. One egg of 60 gram has a water footprint of about 200 litres.

While different production systems can account for a variation in the water footprint of meat, dairy and eggs, so too can different regions of the world have varying water footprints.

Italy, for instance says that the water footprint for its beef production is 25 per cent below the global average.

The Italian meat body Carni Sostenibili said that compared to the world average Italy uses 11,500 litres of water, of which 87 per cent is water from renewable sources and of which only 1,495 litres actually consumed.

The organisation adds that the entire meat sector (beef, poultry and pork) uses 80-90 per cent water resources that are part of the natural water cycle and these are returned to the environment, such as rain water. Just 10-20 per cent of the water needed to produce 1 kg of meat is consumed.

However, on the other hand, the UK’s water footprint is 17,657 litres/kg of which 84 per cent is green water (14,900 litres), 15.2 per cent grey water (2,690 litres) and just 67 litres or 0.4 per cent is blue water.

In the US to produce one pound (1 lb, 0.4kg) of steak requires, on average, 1,799 gallons of water – for pork it is 576 gallons of water and for a pound of chicken it is 468 gallons of water.

Johns Hopkins University says that in general the ratios for water use are approximately 7:1 for beef, 5:1 for pork and 2.5:1 for poultry.

The amount of water used for meat production has raised several questions about sustainability and has seen a growth in research into new production methods and systems that use less and recycle more water.

The international food industry watchdog organisation Food Tank says: “The large water footprints for beef, pork and other meats indicate the large volumes of water used for their production.

“They also suggest a great use of resources beyond water. The question then becomes, why is raising livestock and poultry for meat so resource-intensive?

“The answer is mainly based on the food that livestock eat.

“Here, the water footprint concept can provide some insight.

“What the water footprint reveals is the magnitude of water “hidden” in meat as a tally of all the water consumed at the various steps during production.”

It says that this means the sector needs to look at two areas – feed conversion ratios of livestock production systems and the intensity and scale of production.