Sustain accused consumers and drinks firms of "bottling out" of their duty to protect the environment and tackle climate change by continuing to buy bottled water in record quantities.
The group's new report, published this week, urges consumers to drink tap water "to save the planet". The move may put extra pressure on drinks firms at a time when environmental concerns are in the public spotlight.
Critics say the PET bottles used to make bottled water threaten to create unmanageable amounts of waste because they do not break down over time. Others say merely making and transporting the bottles uses up significant amounts of energy.
Concerns about environmental damage have been trumpeted by the UK government in recent months, but Sustain singled it out for special criticism.
It chided several departments, including the Cabinet Office, Treasury and Department of Health, as well as the House of Commons, for continuing to serve bottled water at meetings.
Others, such as the Food Standards Agency, and Department for Environment, Food and Rural Affairs have switched to tap water.
Sustain also questioned the commitment of drinks firms to using recycled plastic.
A recent project run by the Waste & Resources Action Programme successfully trialled the use of more recycled plastic in PET bottles with some of the UK's biggest retailers and drinks firms.
"However, this remains the exception rather than the rule, so plastic for recycling continues to be transported and used thousands of miles away [eating up extra energy]," Sustain said.
Bottled water firms, headed by Danone, Nestlé and soft drinks associations, have repeatedly hit back at claims they are harming the environment.
Consumers appear to have remained largely indifferent to the concerns. Bottled water sales have soared in the UK over the last few years, despite Sustain estimating one bottle costs around 500 times as much as tap water, which it claims is just as healthy.
Sales have continued to rise by around 6-7 per cent annually.