Look out -- the valve is NO: Normally Open. The water flows when the power to the valve is off. You can wire it up so pressing the footswitch turns the power off to the valve, but be sure to turn the water off manually when leaving the darkroom.
Yeah, I know it's NO. But It is the type of valve I was trying to point out. There are dozens of choices on the site, but I was just trying to get the concept across without actually designing the entire project. The idea is that for less than $50 bux you can have automatic or switched convenience.
I use a similar design except I have an IR photo sensor at the spiggot so when I put my hands under, it turns on by itself.
Gun Control is like: Reducing drunk driving by making it harder for SOBER people to buy cars.