The following is excepted verbatim from coca-coca.com:

Reason #1: Weight or health consciousness
Nearly 30 percent of tap water drinkers at both lunch and dinner cite weight or other health considerations.

Conversion strategy: Offer consumers lighter or non-carbonated beverage alternatives.

Reason #2: Price or value consciousness
Twenty-three percent of lunchtime tap water drinkers, and 13 percent at dinner, cite price or value.

Conversion strategy: Develop and communicate special value offers such as free refills, family pitchers and buy-one-get-one-free offers.

Reason #3: Availability of water (and lack of awareness of other choices)
Twenty percent of tap water drinkers at both lunch and dinner say they "choose" water "because its there."

Conversion strategy: Encourage servers to influence the beverage ordering process to increase consumer awareness of other choices. For instance, offer water to consumers only upon request; highlight value or refill menu messages; advertise with table tents in table service restaurants; plan beverage sampling opportunities for consumers; and train servers and hosts to use suggestive selling techniques or point out beverage choices on the menu.

Note: Consumers who drink tap water based on availability appear to be the easiest to convert to an alternative beverage.

Reason #4: Beverage compatibility with food
About 15 percent of tap water drinkers at lunch and dinner cite beverage compatibility with food as the reason to drink water.

Conversion strategy: Combine or "bundle" relevant food and beverage items together to demonstrate their compatibility. Research indicates that consumers appreciate seeing beverage recommendations next to menu or food items.

Reason #5: Habit
Approximately 15 percent of lunchtime water drinkers, and 21 percent at dinner, choose tap water out of habit.

Conversion strategy: Previously mentioned conversion suggestions can subtly influence consumer purchase decisions in this case. However, research showed that those who drink water out of habit are the least likely to convert.