[ch1234]

How are these scores so vastly different between airlines?

I understand the water sources may vary (by airport? not sure?), but if the planes are largely manufactured by Boeing and Airbus, how are the onboard water sources / distribution systems getting contaminated?

Delta being a 5.00 means they're doing something different, but what is it & what control do they have over the plumbing, water systems, etc.?

[bitmasher9]

Cleaning practices I imagine.

If you have a holding tank of water like in an airplane, and you never clean it, you’re going to have pathogens build up. Just adding in new fresh water isn’t enough.

[kalleboo]

Ask anyone who has worked in a fast food place that has an ice machine

[mlrtime]

Similar reason you often hear that ice machines are full of bacteria... They are seldom fully cleaned by a lot of food places.