What minimum air gap is required between a faucet or supply outlet with a small effective opening (such as ½ inch) and the flood-level rim of the fixture, where nearby walls do not affect it?
Not quite. The answer is D: At least 1 inch, or twice the effective opening's diameter — whichever is greater
Table 603.3.1 scales the gap with the size of the opening it protects: 1 inch for openings up to ½ inch, 1½ inches up to ¾ inch, 2 inches up to 1 inch, and twice the diameter beyond that — which is why the rule reads "at least 1 inch, or twice the effective opening, whichever is greater." Where a wall or rib sits close enough to affect the gap, the table's larger sidewall column applies (1½ inches for the smallest opening, three times the diameter for large ones). A fixture's overflow doesn't substitute for the gap; it solves flooding, not backsiphonage.
Reference: UPC 2021 Table 603.3.1 (Minimum air gaps for water distribution)
Checked against the official text
Checked against the 2021 UPC text. Washington's exam is written against the 2015 edition, which we have not read for this section, so confirm it against your 2015 book.
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