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

head of water • water-head
head of water —body of water kept at a certain height for
supplying a water-mill, etc.: Let us compare a watermill driven
by a head of water, and a windmill driven by the wind.
water-head —
1
. the upper part of a stream near its source:
Passing by the waterhead his father so loved in the old days
of his carriage tours, we drove to the church. 2. = head of
water: Only about one-fifteenth of the total length of the dam,
or 500 feet, will be exposed to the maximum water-head of
85 feet. 3. (sl.) a stupid person; a half-wit: The body, these
waterheads imagine, is a temple that should not be polluted
by animal protein.
Note: 
The expression does not correlate in meaning with the
adjectival compound watery-headed—(arch.) apt to frequently
cry: She objected to the display of emotion … and was apt to
speak of members of her sex as a watery-headed lot.
health food • healthy food
health food —a kind of natural, organic food without chem-
icals: There is greater awareness about health food these days
not just because people want to look good but to prevent car-
diac diseases.
healthy food —food that is low in fat and contains limited
amounts of cholesterol and sodium: More effort had to be
made to improve the accessibility of healthy food in deprived
areas.
heard it from the horse’s mouth • little bird told
me, a
heard it from the horse’s mouth —heard it directly from the
person concerned: The story was even more intriguing when
we heard it from the horse’s mouth.
little bird told me, a —said of information gathered from a
source not to be named: A little bird told me that the appoint-
ment of a director will be made shortly.