Anyone seen the movie Heat? couple of questions

The one with Al Pacino, Val Kilmer and Robert De Niro.

2 questions about the film.

After spending the night with the woman after he meets her De Niro leaves early morning before she wakes up and leaves her a glass of water with a napkin wrapped round it on the bedside table. What's the reason for leaving a glass of water at the bedside for her?

Also, when they are doing the heist at the metals place he sees the cops are onto them and calls it off but how did he know it was LAPD? The next scene he is saying "LAPD where did this heat come from". How did he know it was the LAPD specifically when he never saw anyone and only heard sounds?