Water quality issues in old apartment

I hope this is the right sub, if not let me know. I live in an old farm house (built in 1850), in New York State and our water quality has been off lately. We have a well, there’s 2 apartments upstairs and 2 downstairs. One upstairs apartment has .5ppm ammonia, the other has .25ppm ammonia and 10ppm phosphates, both have a ph of 7.4, downstairs there’s no ammonia or phosphates and the ph is 8.2. Any ideas what could cause this?