The point of this escapes me. A coliform test is a rel cheap test, why try to guesstimate? Since there are several bacteria strains that show up for coliform testing and only 2 are pathogens, why not try to get an accurate reading.
Organic contaminants are usually tested using gas chromatography which is a sort of "sniffer" but much more calibrated.
Water borne pathogens can cause so many diseases that only guessing can be a real limitation especially if youre doing this as a business. I dont believe that there is a valid standard method for "sniffing" coliforms that would stand up to peer scrutiny or be admissable as data.
Besides, many water types impart a different odor due to their chemical makeup. I can have you sniff H2S water that, while full of Sulfo reductans bacteria, will be totally coliform free. Or limestone waters hve a irony smell and some low ph water smells like sulfur also.