The lousy weather in April and not a BBC Panorama documentary was to blame for a slump in bottled water sales, the Bottled Water Information Office has claimed.

On Monday Panorama is set to air an update to its Bottled Water: Who Needs It? programme, which aired in February and included claims from Defra minister Phil Woolas that the amount of money spent in the UK on bottled water was "bordering on morally unacceptable".

The programme is expected to highlight that after the programme sparked a number of campaigns against bottled water, sales dipped in April.

But speaking ahead of the programme, the Bottled Water Information Office said the decline was purely down to the cold weather, including snow in some regions.

"Bottled water sales were up in May and bottled water is more popular than ever before," said spokeswoman Liz Bastone. "Figures for April were down on last year because we had a heatwave in April 2007 but a poor month this year. It clearly shows growth in May, when the weather improved."

Latest data from Nielsen found that in the week to 10 May, sales of bottled water were up 23.2% year-on-year and by 21.7% year-on-year in the week to 17 May. Danone Waters, which claims for every degree change in temperature, water sales are affected by 5%, either up or down, revealed last month that sales of its Evian and Volvic brands were up 22% across the big four supermarkets in the four weeks to 18 May.

"When it is hotter, people turn to water to quench their thirst and hydrate," Bastone added.

The Bottled Water Information Office, which was set up last year to represent UK bottled water suppliers, said it planned to increase its focus on telling the public how the bottled water industry was minimising its environmental impact.

The industry was using 30% less plastic than 15 years ago and was also working closely with national and local government to support recycling initiatives, Bastone added.