12.1 Part 3 Explained: Reading the Water Sizing Drawing and Gathering the 610.7 Data

What L&I and PSI Say About Part 3

Washington's 610.4 amendment keeps the choice of sizing from Table 610.4 or by Appendix A (610.5). The exam exercise uses Table 610.4, the table L&I provides.

What the Drawing Shows

• Meter and street service, the building supply entering the building, the water heater, and the cold and hot mains and branches to each fixture.
• Line types: typically cold water in one line style and hot in another. Check the legend.
• Segment labels (letters or numbers) at each branch point. Questions ask for fixture units or minimum size at a named segment.
• Notes giving the street pressure, the elevation of the highest fixture above the meter, the developed length, the occupancy type (private, public, or assembly), and whether water closets are flushometer or tank type.

The Four Facts Section 610.7 Requires

1. Total fixture units from Table 610.3, with flushometer valves from Table 610.10.
2. Developed length of supply pipe from the meter to the most remote outlet. Developed length is measured along the centerline of pipe and fittings and includes vertical rises.
3. Elevation difference between the meter or other source and the highest fixture or outlet.
4. Street main pressure. Where the pressure fluctuates during the day, design on the minimum pressure available.

Also watch for:

• A pressure regulator: size from 80% of its reduced setting (608.2).
• Devices with pressure loss: filters, softeners, backflow preventers, and tankless heaters. Section 610.2 requires their losses to be included in the pressure calculation.
• Continuous demands such as irrigation or process equipment: add them separately in gpm (Table 610.3 note 5).

A Worksheet Before Any Lookup

Build one line per segment. Record which fixtures it serves, whether it is cold, hot, or both, its fixture units, and its size. Then fill in the one-time values: available pressure, pressure range, and length column.

The Example Building (Used Through Section 12.4)

A one-story office has:

• 2 flushometer water closets (1.6 gpf)
• 1 flushometer urinal (1.0 gpf)
• 2 lavatories (public)
• 1 service (mop) sink (public)
• 1 kitchen sink in a break room (domestic-type sink)
• 1 drinking fountain
• 1 hose bibb
• 1 storage water heater supplying hot water to the lavatories and sinks

The cold main runs from the meter to the water heater tee, then to the restroom, where it splits to the flushometer branch and the lavatory, sink, and fountain branch. The hot main leaves the water heater for the restroom lavatories, the mop sink, and the break-room sink.

How Part 3 Questions Are Usually Phrased

Expect the same handful of question forms, each tied to a segment label on the drawing:

• "How many water supply fixture units are carried by segment ___?" (Section 12.2)
• "What is the minimum size of segment ___?" (Section 12.4)
• "What size meter and building supply are required?" (Section 12.4)
• "Which pressure range and length column of Table 610.4 apply?" (Section 12.3)
• "What is the minimum size of the branch to the flushometer valve?" (Tables 610.3 and 610.10)

Because every size depends on the same pressure range and length column, a mistake in the first lookup repeats in every later answer. Settle those two values first and write them at the top of your scratch paper.

Abbreviations and Symbols to Recognize

Reading Traps to Avoid

• Developed length is not straight-line distance. Add every horizontal run and vertical rise from the meter to the most remote outlet.
• "Most remote" means farthest by developed length, which is not always the highest fixture. Elevation uses the highest outlet. The two can be different fixtures.
• Use the minimum pressure if the drawing gives a range such as "55 to 70 psi."
• Minimum building supply is 3/4 inch even if the table would allow 1/2 inch (610.8).