Nitrite can also be
formed chemically in distribution pipes by Nitrosomonas bacteria during stagnation of
nitrate-containing and oxygen-poor drinking-water in galvanized steel pipes or if
chloramination is used to provide a residual disinfectant and the process is not
sufficiently well controlled.
Chloramination may give rise to the formation of nitrite within the distribution
system, and the concentration of nitrite may increase as the water moves towards the
extremities of the system. Nitrification in distribution systems can increase nitrite
levels, usually by 0.2–1.5 mg of nitrite per litre, but potentially by more than 3 mg of
nitrite per litre (AWWARF, 1995).
Excerpts from: Nitrate and nitrite in drinking-water
Background document for development of
WHO Guidelines for Drinking-water Quality
I'd get a new/different kit or try and find your local water report. I found the Dallas report and it does list nitrite and nitrate at measurable levels, but focuses on contaminants and doesn't list other parameters like hardness or pH etc.