I don't know water coolers, but have you considered using a filter instead? We have a 3 stage countertop filter that works well. We've had it for over 3 years now and it has shown no signs of breaking down. I'm pretty sure replacing filters for it is less expensive than buying water for a cooler.

The one I have doesn't seem to be available anymore, but here's one that seems pretty similar though it's designed to go under the sink rather than on the counter. You can also opt for 1 or 2 stage systems if you want one that takes up less space. I recommend staying with one that takes a standard size filter. That way you get to shop around for better price and/or quality rather than being stuck with what one manufacturer offers. Mine uses 10" filters as does the one I linked.