The BBC has been accused of wasting public money and creating unnecessary environmental damage by spending nearly half a million pounds a year on bottled water. Responding to a freedom of information request from the Guardian, the public broadcaster said it spent £406,000 annually on large bottles for its water coolers.

In addition, BBC staff are allowed to order bottled water for the organisation's hospitality events. The BBC refused to reveal how much it did spend on bottled water at the 103,000 events it held last year, claiming the cost of finding out was more than the Freedom of Information Act required.

Bottled water can also be ordered by staff for internal meetings, provided a meeting lasts more than two hours. The broadcaster said it was assessing the "health issues" of switching from bottled to mains-fed water.

A regional breakdown showed BBC London and Scotland were the biggest spenders, paying £365,368 combined, with the English regions on £23,690, Northern Ireland spending £16,285 and Wales £1,489. The low figure for BBC Wales is because most of its drinking fountains are supplied by mains water.

Steve Bloomfield, senior national officer at Unison, which is campaigning for employers to provide staff with mains-fed water, said: "The BBC could save themselves a lot of money, aside from the urgent sustainability issues. Using the health and safety angle is ridiculous. You might as well say you are going to look at the health and safety issues of using plates. Naturally, normal hygiene issues need to be respected but that applies to all food and drink."

Dave Prentis, Unison's general secretary, said: "Workers work better if they are hydrated and have access to good clean drinking water. Bottled water is no better than mains water and the effect on the environment of all that water being transported around is enormous."

Susie Squires, political director the Taxpayers Alliance said that paying for bottled water was an unnecessary waste of money. "What is wrong with the tap? It is the little things that add up to unacceptable waste at the BBC. Splashing out on bottled water is a frivolous expense. Families are having to cut back on the little luxuries and time the BBC did also."

The BBC defended itself against accusations of wasting licence fee payers' money on an environmentally destructive practice. A spokesperson said: "The BBC is committed to reducing waste and promoting environmentally sound practices. We are also working to implement a policy of replacing bottled water with other options where they are used, for example, in meetings and hospitality functions. Current contractual commitments are being reviewed and the health issues related to replacing bottled water with jugs of tap water are being assessed." The organisation's press office did not provide the figures despite repeated requests. They were only revealed after a Freedom of Information Act request.

Employers have a legal duty to provide staff with drinking water in the workplace, but bottled water has a far higher carbon footprint than mains-fed water. According to Thames Water, a litre of mains water creates about 0.0003kg of CO2, around 600 times less than the 0.185kg generated by a litre of Volvic or the 0.172kg produced by the same volume of Evian. The water cooler bottles used by the BBC are also made from a type of plastic derived from oil, which is not recyclable and takes up to 1,000 years to biodegrade.