I came across this phrase reading E.M.Forster's Maurice,
He(Clive Durham) had neither the blind faith in tutors and lec-tures that was held by Maurice and his set nor the contempt professed by Fetherstonhaugh. "You can always learn something from an older man, even if he hasn't read the latest Germans." They argued a little about Sophocles, then in low water Durham said it was a pose in "us undergraduates" to ignore him and advised Fetherstonhaugh to reread the Ajax with his eye on the characters rather than the author; he would learn more that way, both about Greek grammar and life.
According to Collins dictionary, "low water" means "low tide; a situation of difficulty". Methinks it doesn't really fit in this context. Does it have other meanings?