Up to half of the water used in water coolers across China's capital could be "fake," or not as pure as its manufacturers claim, state media said on Tuesday of the latest in a series of health scares.

The bogus water was either tap water or purified water of miscellaneous small brands poured into empty barrels sealed with quality standard marks, Liu Xiaoyun, the Beijing sales manager of a bottled water brand said.

Liu said the counterfeits began to appear in Beijing in 2002, five years after barrelled, as opposed to bottled, water emerged as an industry.

Four suppliers dominated the water cooler market, Liu was quoted as saying. Of an annual sales volume of at least 200 million barrels, 100 million were counterfeit.

Overall, a barrel of fake water costs bogus producers only 2.5 yuan ($0.33) to 3 yuan, whereas the real ones cost them 6 yuan each. "In either case, a barrel of water is sold at well over 10 yuan in the market."

The lack of supervision had given "leverage" to counterfeit makers in each chain of the production process, from corporate distributors to unauthorised workshops and water delivery stations.

Three years ago, a nationwide inspection on barrelled water found a 22 percent substandard rate. In the most serious case, 80 percent of barrelled water in the southern province of Jiangxi was reportedly not the real thing.