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How do your requirements differ from charity: waters? https://www.charitywater.org/blog/wanna-build-your-own-sensor/ They wouldn't have passed google.org's due diligence if the same could be done with a cheap commercially available meter hooked to a cheap commercially available GSM module.

How turbid is your water? there has to be a point above which treatment at source becomes a necessity, unless of course you are just irrigating with the water..?

At low scale, the best solution could be a trained local user, with an affordable phone (including a stopwatch facility) and a measuring cylinder/bucket, who gets paid per experiment to run whatever flow tests you need & report back by SMS.