Why does the restaurant give me such a small cup when I ask for a water cup, don’t they trust me?! ?

The water in Chicago is unsuitable for drinking, it's tainted with lead.

They probably don't want you dying inside of their establishment.

Honestly, no we dont trust you. We already lost money with the honor system and I dont have time to monitor your activities at the soda machine. If this bothers you, go to better restaurants where you sit and wait for your beverage. You will get your water in a pint glass just like everyone else. 

In short...no they don't. Plus, it doesn't confuse your cup with people paying for drinks.

Yeah they don't you could've killed someone if you had a bigger cup!

It's for specimens.

Yeah, it sucks.  It's like they're saying **** you for getting something that's free.

They don't trust you or anyone else.

they think that you might try to use it to drink soda

They wanna make money by giving you water they make $0 if they gave you a big water that's all you'll drink all night so a small water & then you are more likely to buy a drink!

No. They have no faith in you, nor should they!