The findings come after a YouGov survey found more than 70 per cent of the public feel too awkward to ask for the free water which they are entitled to.
Waste charity Keep Britain Tidy and filtered water brand Brita UK are calling for more public water fountains to help cut down on the billions of plastic bottles thrown away each year.
Around 7.7 billion plastic water bottles are estimated to be bought in the UK each year and only a limited number of them are recycled.
According to the poll of more than 2,000 people, 37 per cent said they felt awkward asking for their reusable bottles to be filled up in places such as bars and cafes even if they are purchasing something.
Only a quarter said they were aware of their legal entitlement to ask for free water in such premises.
Yet the survey also found that 59 per cent of people would be more likely to carry a reusable bottle if tap water refills were more freely available in places such as shops, airports, and parks.
At present, just seven per cent said they usually drank from public water fountains or taps, while only 11 per cent said they asked for tap water from cafes and restaurants.
Bars, theatres, restaurants and other licensed premises are legally required to provide free drinking water on request in England, Scotland, and Wales, although they can charge for the use of any glass.
Allison Odgen-Newton, Keep Britain Tidy chief executive, said: “Topping-up in a glass or refillable bottle would encourage us to stay healthy while helping to reduce littering in our streets, parks and beaches, which is all good.”
Sarah Taylor, MD of BRITA UK, said: “It’s great to see that many cafes, shops and other businesses already proactively offer free drinking water and encourage customers or non-customers to fill up, but we need more businesses to follow in their footsteps, greater availability of public drinking fountains, and to boost people’s understanding of their water rights.”