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by opejn
2757 days ago
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Thank you for sharing your story. I hope you don't mind if I turn it into a thought experiment, because I find it a good example of how tricky finding and fixing a problem can be. I know nothing about water quality standards, so they might be naive, but the following questions stick out to me: * Is there a reasonable contamination hazard from water sitting in pipes that are flushed daily with chlorinated water? In other words, is it vital that there always be residual chlorine 100% of the time, or were the standards designed to accomodate this sort of periodic lapse? * If the dips were harmless, would the inspectors be willing to accept that? * Was the dump solenoid effective at flushing the entire network of pipes, or just the branch containing the sensor? Depending on the answers, the end result could range all the way from "the new system let us eliminate a serious hazard", through "we were probably fine before but now we can be sure at a little extra cost", down to "now we have to waste water to avoid tripping a sensor so we don't get fined, with no actual improvement to the water quality". It's a great example of how what we want, what we test, and what we enforce can get just a little out of alignment, and make a hinderance out of what ought to be a definite improvement. Thanks again for sharing. |
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1)
My understanding is there is very little actual hazard here, provided the pipes are in reasonable shape and there isn't a source of contamination.
One example of a source of contamination: dead ends in plumbing (eg, an old branch that's been capped off). The stagnant water can grow bacterial colonies which can then contaminate everything downstream from where the dead end branches off. The residual chlorine can fight this but it's of course better to not have the dead end at all.
2)
The problem with the dips is it's not possible to distinguish between the "expected" nightly dips and real problems.
For example: do you just ignore all alarms between 3am and 6am? or should that be 7am? Is there another check (+alarm) to be sure the clock is correct (and do you now need a secondary clock source for that) and that DST is respected?
Or do you build something very complex that checks against recent flow rates before raising the alarm -- in which case, how do you test that code and ensure it never breaks (keeping in mind it's safety-related and it's very hard to unit test real-world flow meters, chlorine sensors etc). This gets difficult because you might have different plumbers / maintenance people doing things (adding branches, fixing leaks, etc) that might change the physical layout and not even realize there is control software that might be affected by changes. You can add more sensors to try to check for some of these potential conditions but each sensor costs even more money and adds more complexity.
A lot of this is really "CYA". If something ever did happen and a resident got sick (or worse) from the water, and it came to light that not only were there alarms every night but they were specifically suppressed, even though that might be a rational decision given the facts, at best, that decision would still be faced with a lot of scrutiny and at worse it could be considered criminally negligent.
3)
It's basically not possible to flush the ENTIRE building, because you'd have to open every fixture (every sink, shower, and flush every toilet). In this case, the solenoid dumped water from what was effectively the main line through the building which everything branched from, so from any apartment running the water for maybe a minute would get you fresh water from that main line.
So I'd rank this in the middle of what you said: "quality was probably (usually) fine before, definitely more likely to be fine now, and if an alarm goes off at any time it's real".