not to forget that you need to payback your capital, so in 100 months only you get back your capital. which means you only get profit in 8 years? >.<

they charge an additional 30% ontop of the capital investment? that's daylight robery man!
I thought that there are various types of machine. as some claimed to be RO but might be just those normal filter type or sand filter inside those machine.
secondly, have you put service and maintainence as part of your operating cost? I see most water vending machine are located just outside the permis of the owner's shop. so, if you have a shop of your own, i guess it won't be that difficult to start a water vending business, but if you don't and require to rent space outside some one's shop, then it might be difficult especially when coming to water bill concerns.
lastly, though i've never witness any broken machine myself, there's a tendency for vandalism. hope your machine is insured.