The Verdex Code for Plumbers states that before beginning repair work on a
sewage line in a house, the incoming water valve must be turned off.
However, if the house uses a septic tank instead of city sewage, the Verdex
Code is superseded by an older code (called the Stipex Code) that allows
incoming water to be either off or on. In either case, the rule for turning
incoming water off does not apply when working on commercial property.
If the statements above are true, which of the following statements must also
be true?
A. The Verdex Code is widely observed by professional plumbers.
B. Plumbers working on commercial property must turn the incoming water supply
off.
C. Plumbers must turn the incoming water supply off when working on houses
with septic tanks.
D. Incoming water is considered potable, whereas sewage water is nonpotable.
E. The Stipex Code does not apply to houses connected to city sewage systems.