Trade Exam · Module 2
Plumbing Symbols and Abbreviations
Plumbing drawings speak in symbols and abbreviations, and every office draws them a little differently. This lesson teaches you to start with the legend, gives you the abbreviations you will see on almost every set, explains what common device labels such as PRV, RP and T&P tell you about the work, and covers the pipe identification colors the 2025 California Plumbing Code requires in the field for potable, nonpotable and alternate water systems.
Key Takeaways
- The legend or symbol schedule on the drawing set defines its symbols, line types and abbreviations. Read it before anything else.
- Line styles and valve shapes are not uniform between offices, so never assume a dashed line or a square means the same thing it did on the last job.
- Common abbreviations: WC water closet, LAV lavatory, KS kitchen sink, CO cleanout, FD floor drain, VTR vent through roof, CW and HW cold and hot water, DWV drain, waste and vent, PRV pressure reducing valve, T&P temperature and pressure relief valve.
- Some abbreviations have more than one meaning (SW can be soft water or storm water; WC is also used for water column in gas work). Use the legend and the context.
- A PRV on the plans means pressure regulation; CPC 608.2 requires a regulator where static pressure exceeds 80 psi, with an expansion tank downstream.
- An RP (reduced-pressure principle assembly) has two check valves, a relief valve, four test cocks and two isolation valves (CPC 603.3.7). Plan for its drain line and its location.
- Field identification colors (CPC 601.3): potable water green with white lettering; nonpotable yellow with black lettering; alternate water sources such as gray water and recycled water purple.
Why This Matters
CSLB lists "shop drawings, plans, and specifications" as a subject in Planning and Estimating, which it weights at about 22 percent of the C-36 trade exam. Symbols and abbreviations are how drawings carry information. If you misread one, you can miss a device in your takeoff, rough it in the wrong place, or leave a code item out of your price.
Start With the Legend
Every professional drawing set has a legend or symbol schedule, usually on the first sheet of the plumbing drawings or on a general notes sheet. It lists the symbols, line types and abbreviations used in that set and what they mean.
Offices do not all draw the same way. Differences you will run into:
- Line types: one office draws hot water as a dashed line, another uses a different pattern or a label.
- Valve and device symbols: there are several ways to draw a valve; the legend says which one this set uses.
- Fixture symbols: some sets draw fixtures to scale in outline, others use simple symbols with a tag.
- Abbreviation style: DWV, D/W/V or separate D, W and V tags.
When the legend and your habits disagree, the legend wins. When the legend does not cover a symbol, ask the designer with a written request for information rather than guessing.
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