Do you want to cover the whole thing or just the top. I'd probably find some nice quilted material and cut out a circle to fit over the top. Maybe you could make your own pattern with paper. Good Luck !

Would any of these work?
The website is selling them already made but I don't think it would be hard at all to figure out how to make them.

Here is a link that might be useful: Cooler Covers

Have you made your watercooler cover yet? If so how did it turn out? I want to make one for my cooler also but I am waiting to see how your's turned out and if not good what would you do different next time? Did you line it with muslin? I have been thinking about making one with quilted fabric to give it more body. What do you think?.......Di

I am not sure what you are looking for but I covered the bottle part of mine with a printed green chino fabric that matched my colours, and made a "bag catcher" to match for plastic grocery bags. If you look on ebay for water cooler covers there are many there. Took about a half hour to make them both. Just a tube of fabric with elastic pulling it closed, tight on the top and just loose enough to pull over the bottle.

My sister used to make them...she drew her own pattern and sold many of them! Easy enough ot make the pattern.