Very interesting points in this thread:

> Testing your irrigation water won't keep the feedlot next door from blowing dried-up cow shit dust all over your lettuce. (Or, you know, into your irrigation water on a day when you're not testing). [1]

> It won't keep harvest crew co's from putting so much time pressure on crews that they can't clean their harvest rigs properly between shifts. [2]

> And it sure won't solve our traceability problem. There's no way in hell we're having this much trouble tracing the lettuce to its source, unless there's massive supply chain fraud going on. We should be worried about THAT. [3]

This one reminds me of a situation I ran into once:

> (You also have to ask, WHY would a farm or any other business target their testing towards when they're likely to get red flags? They don't want that. Any time you do testing, there are lots of ways to game it to lean towards clean results. Which is what farms & companies want.) [4]

We were installing a drinking water monitoring system at a rural retirement home (on well water), probably a couple hundred residents.

Up to that point, one of the tests they did was a manual daily chlorine level check. Essentially you need to have a certain amount of residual chlorine in the water at the point of use, which lets you know you you are putting enough in (if you put too little in, it gets used up as it's breaking down organics in the water, and you end up with a zero). If the level is too low, you have to report it and explain what happened and how you fixed it, and if it happens too much, inspectors will start looking closely at your practices and forcing fixes and basically nobody likes that.

The new system had continuous monitoring of several parameters, one of them being chlorine, and would record everything as well as send alerts to people if anything dangerous happened. The chlorine monitor was installed at the opposite end of the building from the water supply, trying be representative of the worst case 'point of use' level.

As soon as it was online, it started sending alerts every night in the middle of the night. The free chlorine level would drop starting late in the evening (as the usage dropped), and then somewhere between 2 and 5 am would drop below the alarm threshold, and around 6-7 am jump back to normal. The owner was pissed that we had screwed the system up, because they didn't have this problem before the monitoring system was in.

Of course what was happening was not new, it was just that as usage dropped off as the residents went to bed, the water in the pipes just sat stagnant, and residual chlorine was slowly used up to the point there was none left. The daily checks were usually done mid-morning, after there was a lot of use as everyone woke up, and so all the water in the lines was freshly chlorinated when the check was done.

For years, anyone getting water in the middle of the night was drinking technically unsafe water (it still had been treated and likely posed no real health risk, so long as there was no contamination in any of the pipes or fixtures), and all that happened was the situation was exposed.

We eventually added a solenoid to the end of the line, and programmed it so it would open and dump water when the chlorine level got low but before the alarm threshold, at least getting fresh water into the main distribution lines of the building and avoiding the alarm condition.

It always stuck with me that the owners reaction was not "Oh, thank you for finding and fixing a problem I didn't even know about before it got someone really sick" but more like "your stupid system made things WORSE, we should rip it out and go back to how it was before."

[1] https://mobile.twitter.com/SarahTaber_bww/status/10670961003...

[2] https://mobile.twitter.com/SarahTaber_bww/status/10670961010...

[3] https://mobile.twitter.com/SarahTaber_bww/status/10670961017...

[4] https://mobile.twitter.com/SarahTaber_bww/status/10670961060...