Is it true that UK businesses are required by law to provide employees with drinking water?
Actually it's true! A 1992 Workplace Regulation stipulates that "an adequate supply of wholesome drinking water shall be provided for all persons at work in the workplace" and that employers must also "provided a sufficient number of suitable cups".
The easiest way to satisfy this requirement is to install a water cooler/dispenser in your place of business. You can choose from a bottled water cooler or a plumbed in water dispenser. Check with suppliers and compare quotes to get yourself the best possible deal.