I read on another site that at MK, CMs fill up their water bottles at the front of Guest Services. There are two water fountains and CM's use the left hand side one, due to it has a filter on it. Are there any others in other parks that have filters on the water fountains?

This is really interesting.

I have never heard of this, but filtered water in the MK would be a welcome amenity.

I would expect that CMs usually filled their water bottles offstage, though.

having had seen what tap water is like in orlando (off property), i have never had any problems with WDW water fountains except for those that aren't working properly (they're either warm or don't shoot the water high enough).

to be blunt, i wasn't aware most cast members carry water bottles. nor would it be practical for them to constantly be going to the front of the park to fill it up (something i doubt disney would allow on their dime anyway) and if it was meant to be some sort of secret, it would be backstage.

other than the fountains that aren't working properly, i wouldn't believe any particular fountain was better than others.

There is always filtered water available to the CMs backstage. Depending on the location it will either be bottled (in 5 gallon jugs) water or a dispenser with a line running to it but with filters in ther dispenser. There is always something in the break rooms, but in most outdoor areas there is a very close by offstage location.

I personnaly have two water bottles that I will freeze at home. I start using one in the morning, adding water as needed. By the time I'm at my lunch break the ice inside has fully melted and I will then use the other one in the afternoon.