How to create a night-activated fountain in minecraft

Build your physical fountain. This can look like whatever, I just chose an appearance I fancied.

Add a block on the back connected to an extended sticky piston. The sticky piston should be powered by the daylight sensor, as shown above.

Add a chute of water so that when the block is released, the water will flow out of the fountain.

Wait for day to become night, and watch as the water flows out of the fountain!