Make a unit disappear for a certain amount of time?

[Hildagarn]

I have this Water Elemental Hero and one his abilities is to turn into water and rush to a point, then reform into the elemental.
I know the Water would be a unit and you would move it to the casted point, but how do you make the elemental disappear until the water gets to the point?

 

[Executor]

Unit - Hide Unit

 

[Hildagarn]

.....wow...thats simple XD