Does anyone know of a place to order solenoid valves for standard kitchen / bathroom sinks?
Something like this:
Somewhere I don't have to buy 500 pieces...
Try made-in-china.com, most sellers will cooperate on a few units for you to evaluate before placing a main order.
Most advertise samples available for sale, looking like a legitimate business and not a hobby electronics person sometimes helps = )
Have you tried e-bay. Entering "solenoid valve" (without the quotes) brings up loads of inexpensive options
jack
While not exactly what you may normally consider (and I am not sure they can handle hot water well; also, there may be code issues!), have you thought about using standard sprinkler valves? They are fairly cheap (although if this is for your house, I would spend the money and purchase commercial-grade brass solenoid valves, which tend to be more expensive), although bulkier than other solenoid valves, of course.
I looked into this sort of thing when I first started Arduino. It depends on the flow requirements you have, but the cheapest I found were sprinkler solenoids, as cr0sh suggests. They tend to run on 24VDC with a hell of a current to hold open. Better designs are "pulse and hold" which needs less power but they're usually more expensive, too. The page you linked doesn't say much about the actual specs.
There's an ebay storefront for a two-person company in Arizona, who will sell individual 12VDC units for around $20. I made a board to control eight of them by I2C.
Something that I wasn't clear enough on - I mentioned "there may be code isssues"; what I meant by that is that, depending on the laws in your area, it may not be "legal" to install sprinkler parts into a system that could potentially be used as a source of "drinking water".
By "legal", I mean you could get away with it, until you (or a buyer) have to have the house inspected for a sale (should that occur); it might fail, you might be fined, at a minimum you will have to replace everything if it isn't "up to code". So check with your local building laws to see if that is something you care about.
Also remember my concern on whether such valves could be used with hot water; this I don't know. I would imagine that they aren't spec'd for use with hot water, nor are the parts rated for such usage, simply because sprinklers don't use hot water. You wouldn't want such a system to fail (of course, when you least expect it, like when you are on vacation). Also know that sprinkler valves (like all valves, but sprinkler valves seem especially prone) fail; keep that in mind as you build your project - you might want to set something up (in-floor drain?) to handle such an issue, if it is a concern. Otherwise, keep your homeowner's coverage up!
They are 12v and are made for use with water lines.
Dan