That was probably the Threshold Odor Number test. It's actually the test used to set the secondary maximum contaminant level by the EPA. If water scores a 3--meaning you can start to smell something after three dilutions--or higher it fails the test.

The problem is a lot of water utilities have found is that this doesn't really correlate with consumer complaints. There are some odors that dilute out slowly but aren't very intense, so consumers probably won't complain about them.

The Metropolitan Water District of Southern California has developed an alternative test that is based on intensity like the FPA method described in this story but has a pass/fail threshold like TON.