It sounds like what you need is a solenoid valve that just turns on and off very quickly. Doing this is a small line that has little pressure in the line should enable you to get a small amount of water through the solenoid and to "drip" into your pool creating the effect you wish.
The solenoid is can be air or electrically actuated to turn on and off. It sounds like you would need electric, hooked up to a timer.
have the architect stick his pinky on the outlet pipe and get exactly the amount of trickling desired...
or you can use a needle valve as suggested by hero123, swagelok is a good place to get acquainted with needle valves...there is a wealth of available designs for all kind of applications.
HTH
Saludos
a.