When you do tests, are you rinsing your testing vial 3 times with DI water after testing?
And how are you washing your test kit vials?
When I worked at a water supplier, in order to "not get" skewed results, we (and all other certified labs) would rinse the vial at least 3 times with DI water, and at the end of the day, all glassware would be acid washed to remove residue.
This was not only done for nitrate, but any other test, pH, alkalinity, etc etc.
When testing for nitrate we used a photospectrometer that cost more than my truck, and ran a DI blank, a 2ppm standard, and a number of samples, rinsing with DI water 3 times between each, to assure accuracy.
Reagents residue builds up, nitrate collects in interstitial spaces in plastic and glass, and can easily causes false readings. If you do not practice the above aseptic techniques, and your results differ from your water company, well......
Now if you are on your own private well, that's different, but if you are on a municipal supply, as Drstrangelove already said, the high readings you get would be grounds for serious consequences for the supplier.
That may be different of course, if your politicians decided to go he Flint route, and opt for money over the health of its citizens.
