The funding splash marks the biggest single investment in the family-owned company's 11-year history. The new Krones bottling system is the first of its type in the UK, said the company.
Work has already begun on the 23,000 sq ft extension to the existing building in Harrogate, North Yorkshire, to more than double the current facility. Completion is due in February 2014.
Investment follows record-breaking trading periods for the company, which saw gross sales of 10m bottles sold in July.
Water Brand consistently outperformed market growth in the bottled-water category, seeing business grow 16% in the last financial year to over £8m.
Managing director James Cain said: "The bottled water market has never been in a better position: it is now valued at an estimated £1.7bn.
"Growth is down to the public becoming disillusioned with sugary soft drinks, coupled with a continued move towards healthier hydration. And of course good weather always helps.
"We now need to safeguard and further enhance our offering, which is why we're investing 6m in the most technologically advanced equipment available to significantly increase capacity."
