Simplified Arduino Shower Timer - as a roommate gag

I have yet to build an Arduino system, but I am very intrigued.

I am trying to build a very simple shower timer, but more as a gag joke rather than for function. I live with two dudes in our late 20's. One guy always takes crazy long showers, we give him crap about it all the time but he won't stop. The last person to wake up has zero hot water. My other roommate and I are very DIY so we want to create a hidden system that will cut the water after, say 5 minutes. But we also want a simple toggle switch to override the system. We plan to install the water shut off valve on the pipes near the water heater.

So, my question, Could I use the following two items to monitor when water flow starts and then cut the water flow after five minutes using an Arduino board? What Arduino board would I need? How about power supplies or anything else?

http://www.ebay.com/itm/G3-4-Water-Flow-Sensor-Switch-Hall-Effect-Flow-Meter-Counter-1-60L-min-v-h9-/321227692244

http://www.ebay.com/itm/DC12V-Water-Air-Gas-Fuel-NO-Normal-Open-Solenoid-Valve-3-4-BSPP-Flow-20mm-/271229917810?pt=LH_DefaultDomain_0&hash=item3f26901a72

Be sure to put the shutoff valve on the hot water pipe. Unless you really mean business ;-)

Instead of the flow meter, you can detect if the shower is in use using a thermometer up against the shower pipe (and some software to prevent oscillations, unless those are desirable :-P ), since you don't care if he takes a long cold shower. Less plumbing and cheaper.

(Also, when you move out, bonus points if you can figure out a way to make it wait a few months before re-activating itself - I can think of one way that's not dependent on continuous power, though very unpredictable).

I will need to plumb into the hot water line coming from the heater to put the shut off valve in, so plumbing in the flow sensor won't be an issue. I plan to set this up as a bypass from the main pipe so it will be easier to remove.

What about power supply and an Arduino board? Will the Uno work? How do I bring power to the board, sensor, and valve?

It looks like the water valve only has a + and - coming out of it. So, I assume I will need a relay to activate that? If so, any recommendations?

I would offer that you could use a motorized ball valve and a temperature sensor.

slowly start shutting off the hot water after 4 minutes with a near complete shut off at 6. then a full on hot for 20 seconds, back to a near off hot. followed by 2 minutes of mostly hot.

the first cold burp will indicate that there is something odd about the water heater, like it has a cold spot. then the warm water flows for a couple minutes, then it goes cold again.

Pavlovs dog would have one start to relax then realize time is of the essence to get soaped up and rinsed off .

ebay 271229940396

http://www.ebay.com/itm/271229940396

the great part about the arduino is that you can add a switch anywhere., even a wireless switch

I think that if you can manage it, he will believe there is some odd thing about the water heater. now to create s web page about water heaters that go hot, cold, hot, cold.......

for testing, I would think that a pair of valves that work in reverse from each other. one adding cold water while the other restricting the hot that way if he shuts off the cold completely, there would not be any apparent volume change. a shutting off of the hot water that lead to a reduction in flow would be a dead giveaway.

Oh the joys of youthful pranks.