The way most servers ask “would you like any water?” gets a 60% “just tap, thanks” response. Re-frame the question and the same table accepts a $5–$8 jug 80% of the time.
The line
“Should I bring a jug of sparkling for the table to start, or would you prefer still?”
The two choices both contain a paid product. Tap water is no longer the offered option. It’s still given on request — you don’t refuse — but you stop offering it as the path of least resistance.
Train it once
Pre-shift briefing, demonstrate the line twice, role-play once. The whole training is 4 minutes. The lift is permanent.