The simplest and cheapest solution that you can have. It might even make the user appreciate the water even more when you have to work a little to get it out.
Wit the pump comes a non-return valve that will make water flow upon the first pump-movement. We enclose a ⅜” to 8mm John Guest fitting that will make it easy to connect to your system. You just need to cut off the hose connection to mount the fitting at allow the 8mm hose to be pushed in.
The pump will give 3-4 liters per minute, so a glass of water will not take long.