The former UN climate chief who has advocated putting a price on carbon emissions says water also should carry an appropriate cost.

Water should be priced higher to avoid waste, a climate expert told a water seminar. (istock)In a world where supplies of fresh water are shrinking, countries, companies and individuals should be aware of the value of water, Yvo de Boer told a water seminar in Brussels, Belgium, on Thursday.

It takes 75 litres of water to make a glass of beer; 2,700 litres to manufacture a T-shirt and 16,000 litres to produce a kilogram of beef.

At the same time, UN figures show, about 2.5 billion people, nearly half the Earth's population, have no access to sanitation, de Boer said.

"Part of the reason we are seeing so much wastage of water in a number of countries is because water is inadequately priced," he said. Few countries have economic incentives to use water sensibly.

Water supplies are becoming less reliable in many places around the world while the global population and food demands are growing, de Boer said. As local climates change, scientists say water shortages will become more severe in some of the poorest countries, which could lead to mass migrations and international conflict.

Former UN climate chief Yvo de Boer now advises companies on how to make their operations more sustainable. (Anja Niedringhaus/Associated Press)De Boer, who resigned as head of the UN climate change secretariat in July, is now a consultant for KPMG, advising companies on making their operations more sustainable.

Calculating the input of water in the production process — a product's water footprint — should become standard practice, he said.

"There are parts of the world where perhaps water footprinting will be more important than carbon footprinting," he said.

De Boer did not say how the price of water should be set, although he thinks it should be determined according to local conditions. He recalled seeing a sign over a toilet in a Middle Eastern country that said, "When you flush, remember a litre of water costs more than a litre of petrol."