Steve,
We both get our water from SOCWA, I'm in Clawson. SOCWA buys the water from Detroit. Both Detroit and SOCWA treat the water with 100% Chlorine gas and SOCWA monitors chlorine residuals daily to keep the chlorine content within the allowable limits. My tap tests 0.00ppm for ammonia. If organic material with a Nitrogen content gets into the water system, it will react with chlorine and form chloramines and ammonia. The organic material could get into the system thru a cross connection, watermain break, work on the water system, opening a fire hydrant, etc.