Best Water Purifiers

I was thinking of purchasing a red ear slider turtle but I have a few questions:

When a turtle is bought, how long is okay for it to go without water? (by travel, etc.)

Also, is it absolutely necessary to keep it in a glass terrarium with a water filter? Or can I make a little terrarium out of a plastic one, making a realistic habitat, and changing the water frequently?

I have a travel Berkey water filtration system. I put the filter away for a few months, and when I got it out again, a rust-colored, mildew-appearing substance had grown on the outside of the black filtration elements. What do I have to do to make them usable again, or should I buy new ones?

First time traveler to Kenya and going on a religous mission.
What shots will I need?
What kind of gear should I bring? netting? water filters?
Passport information?
etc!
Any and all information or ideas, suggestions would be greatly appreciated!