If the animation of the sprite isn't important you could set a random animation speed for each sprite, then when sprite animation frame is 2 spawn water droplet.
If anims must all be same speed you should be able to start a timer for each sprite of a random value then say sprite on timer start animation, this will pick the correct sprite. Then have sprite frame animation is 2 spawn droplet. Do not use a for each with the on timer condition as you described.