this is a very easy prank to do, and its hilarious to watch.

as long has you have a sink and one of the little sprayers you can easily pull this off
(the sprayer is the silver tube, farthest to the right in the picture)

Step 1: Materials

1)A sink (probably gonna be one in your kitchen)

2)a sink sprayer

3)A rubber band or clear tape both would work(clear tape would be more discrete)

Step 2: Assembly

take the clear tape(or rubber band) and rap it tightly around the trigger of the sprayer and the sprayer tube. this will make it so that when the sink is turned on the sprayer will start spraying

Step 3: Have a Good Laugh

once somebody turns on the sink the sprayer will be turned on as well covering the person in water.
(the sprayer needs to be pointed in the direction of the person your pranking)

have fun