My impression is that the average dinosaur would be markedly less dependent on lakes and rivers than the average mammal what with excreting their equivalent of urine as a whitish paste along with their faeces and an impermeable scaly/feathery skin substantially decreasing water losses.
Of course, sheer size helps, too, by decreasing the ratio of surface to volume.
The same effect makes it more difficult to get rid of heat, but the air sac system should take care of that.
Still the same effect makes it more difficult to take up heat from the environment...