That's a bad idea. Why would we pay for that when it's already free for the asking? All you have to do is ask the waitress for lemon when you get your water. I've been drinking water that way for decades. I never order beverages in a restaurant; I always ask for plain water and lemon. It's free. Let's NOT put it on the menu and start charging folks – they already upcharge for all the other beverages.

Factual example: We used to own a café, 2000-2006. So, we know the actual cost of those sugared beverages. Soda costs pennies per cup (including the cup) – but food establishments sell it for dollars per cup (and charge you for the cup – which back then was less than a penny per cup – if you ask for water). The reason the make you think they're giving you a beverage free with your meal is that everything in that meal is already upcharged individually on the menu by around 150% over costs. Those combos are still upwards of 100% retail markup – including the "free" drink.