A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

Note: 
The expression does not fully correlate in meaning with
the phrase at low water—
1
. when the tide is out and far from
the shore: Filey Brig is a remarkable ridge of rocks, projecting
half a mile into the sea and perfectly dry at low water. 2. (also:
at low water-mark) = in low water: The money market was
very tight; but in 
1
905 everything was even worse, everything
was at low water.
in demand • on demand
in demand —(of goods, services, etc.) desirable; much sought-
after: Crops such as cotton were in demand around the world.
on demand —whenever requested: A demand deposit means
that the customer can withdraw his money on demand.
in depth • out of one’s depth
in depth — dealing with a subject very thoroughly: He had
the choice of writing in depth about a few novelists or of skim-
ming over as many authors as he could.
out of one’s depth —in a situation too difficult to understand
or cope with: When John talks about music, I soon get out
of my depth because he knows so much more about it.
in disorder • not in order
in disorder —showing absence of order; in confusion: Inves-
tigators said they found some of his personal belongings and
papers in disorder.
not in order —(also: out of order) 
1
. (of a machine, etc.) not
working properly: Noting that the elevator is not in order,
she dials for a repairman and waits for his arrival. 2. (of a pass-
port, etc.) not valid; not as it should be: Joel apparently could
not stay in Istanbul (he was deported as his papers were not
in order)…. 3. (formal) not in conformity with the prescribed
mode of behavior: It is not in order to interrupt and the Sen-
ator would not have been interrupted had I been in the Chair.