As an American (Los Angeles) I think the main difference between how I pronounce water and the way Judi Dench does it is the t. We treat the t like our brake pedal at a stop sign with no other cars around, barely a tap, basically a d sound. The a we pronounce ah. Judi’s ah sounds similar but maybe a little oh-ish to us.Then of course there’s the -er, which we do pronounce, while Judi says -uh, in the classiest way evah of course!