Volunteered to supervise our building’s backflow inspection yesterday. What a fascinating distributed maintenance institution!
Big buildings have special valves to keep building water from being siphoned into the water supply. In SF, each has to be manually tested annually!
Conversation
It’s a neat variation of “how many piano tuners in Chicago?”. There are a lot of condos in SF! 10^5 is probably the right order. Test took 30m; with transit maybe one plumber can do 10 tests per day. That’s ~2500 tests/year/plumber: ~40 full-time backflow testers!
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And that’s just residential—apparently the tests get more complex for commercial and industrial, since backflow may not only pollute but contaminate the water supply.
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