Water Tank for Concession sales

We operate a small concession stand and sell a lot of bottled water over the weekend. About 25 gallons worth of plastic bottles. We have had a couple of folks ask us about a clean water supply - they will bring their own environmentally friendly bottles to fill and we will charge by the volume.

We need a portable tank that is collapsible and is fairly small in size and figure a 25 gallon water capacity. It is very important that is is clean and sanitary and does not taint the water. We will fill the collapsible tank with clean filtered water and need a 2 inch fill inlet and then dispense through a small valve, perhaps a 1/2 inch?

We think this will work great in our area as folks tend to take to being frugal with resources.