Had a problem last year with tilly who become very ill for unknown reasons to me,sickness and diarohea bless her was caused through tilly drinking from puddles in the woods,my goodness it was very worrying for us all,but the vets obviously have seen the symptons many times previously and after some injections and course of tablets she fought it off,i would never like to see that happen to anyone,so please take note from the original poster of the harm that is hiding in water.
We are often asked if tilly is a lake dog,i never let her near any lake as i am not a good swimmer and wouldnt want to take any chances with her in case of problems that could arise.