one other thing I learned about water with nitrites or nitrates- it could be from microbiological contamination, too.. kinda backed up in that article:

"Nitrates form when microorganisms break down fertilizers, decaying plants, manures or other organic residues. Usually plants take up these nitrates, but sometimes rain or irrigation water can leach them into groundwater. Although nitrate occurs naturally in some groundwater, in most cases higher levels are thought to result from human activities. Common sources of nitrate include:"

They cover that it comes from those sources, and can leach into groundwater- but it also can be directly from biologics in the water..

so any water that tests positive for nitrites/nitrates should be treated as though there are bugs in it, or else