"Advertising," as it's often defined, "is the creation of wants."
In summer in Japan, though, there's little need to create a demand for cool drinks. But if you're a supplier, there's every incentive to create a demand for your particular product. And when products are basically very similar, like brands of bottled water, advertising agencies make hay (especially while the sun shines) trying to distinguish their client's version from the others.
In doing this, their job is made a little easier because this highly competitive, 116 billion yen-a-year market has two basic divisions: one between big bottles for family use, which account for 80 percent of sales, and small ones for personal use, which soak up the rest; the other between imported and domestic water, with imports now running at around 20 percent.