What makes us keep reading? What makes us care about what happens to a character?
I think it ties in to the idea that a story (and a character) needs an agenda. A goal.
But why would a character needing a glass of water create identification? Well, apart from the fact that we've all been thirsty, what creates the tension is not the WANT it's the obstacle. Something or someone keeping a thirsty character from that cool, refreshing drink.
But what if the character just gives up. Strolls on and thinks, I'll get a drink later?
There's two issues there, I think. First you have to UP THE STAKES. Make them desperate for water...and not just because it's been a day and a half in the dried up drought of the desert, but also, maybe, they've got a sick, thirsty child to save. Or something.
Also very important (I think) is that the character does not give up. Boldness.
I think reader identification is as much envy of characters who attempt to take control of their lives as it is about recognising and sharing goals. Wish fulfilment.
Like those Twilight books where the teeneage girl wins the love of the cold marble-chested vampire.
So...let's have characters with a goal, with a lot at stake (no pun intended, vampire lovers) and who will go for it and not give up. Who can't afford to give up after that first step. No matter what the obstacle and what shit you throw at him or her.
And it's your duty (as writer) to throw a lot of shit.