It varies on where you go for food. Most quick service places will you a child size cup when you ask for a "water cup". At Plaza Inn where they have the big plastic cups, you can fill it with ice water from the self serve drink dispenser. Over at Boardwalk Pizza & Pasta in DCA, they also have SS drink dispensers and we have been able to fill regular size disposable paper cups with ice and water without any issues, same with Pizza Port in DL. Rancho Zocalo at DL also has the drink dispensers, however they ask you take a small plastic cup they have at the registers.