What does a fixture unit represent in cold water design?

• A. The physical size of a pipe
• B. A unit value representing a fixture's water demand
• C. The pressure rating of a pipe
• D. The color coding of cold water lines

Answer: (B)

The main idea being tested is how designers measure and compare the water demand of different fixtures. A fixture unit is a standardized value that represents how much water a fixture is likely to use during typical or peak usage. In cold-water design, each fixture is given a fixture-unit value, and you sum these values for all fixtures served by a portion of the system to estimate the total demand. That total then guides how large the pipes and the supply should be and what pressures are needed. This approach focuses on how much water is demanded, not on the physical size of pipes, their pressure ratings, or color coding. The fixture-unit concept lets you account for simultaneous use—some fixtures may run at once while others do not—by converting diverse fixtures into a common scale so the system can be sized appropriately.