Only when TSA is providing security for the flight - ie. US flights.
I've had contact lens solution confiscated from me in Heathrow (London). I was bummed and annoyed at myself that I hadn't anticipated that. I've learned to check my bigger bottle (if checking) or carry on multiple small ones (if doing carry on only). The solution I use isn't readily available.
CATSA (Canadian airports) also exempts saline solution.
But yes, definitely check the rules for the country you are flying out of.

You're joking, right? I hope so, but I'll play along. Water is a liquid (we learned that in elementary school, or through life's observations). There is water in deli meat and deli meat, is unlike crackers which contain a negligible amount of water. Often people also have lettuce, cheese, sauce, or other vegetables on sandwiches. These items also contain a significant amount water. Ever cook down a tomato until it no long steams? I have, it's microscopic relative to it's original size. They are therefore, more liquid-like than say, chips.
Hungry flyers everywhere, unite!