My understanding is the water tested in this study is the water in the lavatory faucet and what they use to make hot beverages onboard. If you ask a flight attendant for water you would always get water from a can/bottle/box depending on airline, at least based on my limited experience.

- "The ADWR requires airlines to take samples from their water tanks to test for coliform bacteria and possible E. coli."

I believe the study is based on water in the tank of the passenger airline and the advice given is to not drink that water, on average.

They tested the water from the tanks, which apparently is used to prepare hot drinks.