Solenoid valve. Get from McMaster or any supplier of inground sprinkler
systems.

Tried that on my dog. There is a slight time delay from the time the
valve acuates until the pressure builds up sufficiently to get a good
spray going. The dog learned to bark, wait for the first little sounds
from the solenoid, high tail it for his dog house. After the first
couple of nights, he didn't even get wet. Bought a shock collar for
field traing, left it on all night, blipped the controller from my bed.
About 2 nights and no barking. (Except when the deer stroll by his dog
kennel!)

Steve B wrote:

I want to get a valve that is opened and closed instantly by an electric
current. It will be put on a pressurized garden hose. When I hit a button,
the valve will open instantly, and water will spray out the hose. When I
let off the button, the valve will close, and the water will shut off.

I'm trying to make a simple system to help break my dog of barking.

What is the name of this valve/actuator/device? And where might I find one?

Steve