The group, which have published the research in the August edition of its own self-titled publication, said that 50 per cent of those surveyed could not taste the difference between tap and bottled water. An additional 18 per cent of the 3,039 online respondents said they actually preferred the taste of a publicly sourced supply, Which? said.
The findings form part of growing criticism leveled at the bottled water industry, regarding the social and environmental impacts of the product amidst rapid consumption growth. Bottled water groups say most of the attacks are 'misinformed'.
The report concludes that consumers, to the likely detriment of water bottlers, would be better served by free to use, vending machine like, refill points in public spaces. The watchdog claims that 10 such installations are already planned as part of a pilot scheme in London.
Neil Fowler, Editor for which?, said that markets like the UK that already boast safe and high quality drinking water have little need for bottle alternatives.
"There are plenty of good reasons for choosing tap water," he stated. "You can save money, it's better for the environment and it can taste just as good - if not better."
The bottled water industry has been quick to respond to the growing levels of criticism being faced on the industry though.
Stephen Kay, communications director for the International Bottled Water Association (IBWA) told BeverageDaily.com earlier this year that growing criticism from environmental groups and politicians alike had 'distorted' the real impact of growing bottled water consumption.
"Consumers are not uniformly replacing tap water with bottled water; rather they are choosing bottled water over the other beverages available at the store and home," he said.
Despite the criticism, current estimates on potential growth of bottled waters remain buoyant, according to findings by consumer analyst Zenith international.
If the current market growth continues, global consumption of the product is expected to grow to 251bn litres by 2011 from 187bn litres in 2006, Zenith added.
This potential is coming in part from growing innovation within the bottled water market, particular for added-value waters that claim to offer nutritional or cosmetic benefits.
In Western Europe alone, functional water consumption rose to an estimated 273m litres in 2006 from just 30m litres in 2000, Zenith said.
Beyond the perceived social impacts of this growth, environmentalists have also expressed concern over how the bottled water market is affecting the environment through packaging waste.
San Franciso's mayor Gavin Newsom last year announced a ban on the cities departments using money to buy bottled water, while New York officials are urging consumption of tap water to cut down on the cities high levels of packaging waste.