[gricardo99]

Update: with "=" filtering ("at or above minimum reporting level"), AND... using "Contaminant" instead of "Disinfectant Type" (I followed a comment that seems to be off...always worth checking for yourself!).

for pwsid in $(grep 48103 UCMR3_ZipCodes.txt | cut -f 1);do grep $pwsid UCMR3_All.txt | cut -f 14,17 | grep =;done | sort | uniq