Difference between the wave forms in the water and in the Young double slit experiment We can observe when we cause a slight disturbance at two points on the water surface which is intially totally undisturbed , it will form water waves which would look like as shown in below image:

we can observe that there are constructive and destructive interferences at some places and also which lies in between these type of interferences (that is between fully destructive and fully constructive) . We notice that it doesnt need screen to show the interference effects at all , so why in YDSE we need screen to show the interference patterns, is it because we cant be able to observe the interference being happen in air or any other medium from our naked eyes?
 A: The screen is used simply because it makes the interference effect easier to see and to record and analyse. As is the case with the picture of the interference of water waves which you included in your question, the light interferes with itself everywhere. The use of a screen allows you to see the interference along a straight line, measure the fringes at a fixed distance from the slits, photograph them, and so on.
A: You need the screen because you do not want to stare in the sun with your eyes even if you were doing it through a peep-hole. Imagine adjusting the size of the diaphragm (of the slits) to see if there is already enough light has already fallen on your retina.
A: Did you know that a water wave in a single slit will NOT make an interference pattern ... but light will!  Water and light are similar but also very different. In the DSE there is NO light in the dark areas .... photons will travel to areas that are more "resonant" (path length is a multiple of wavelength), this is quantum mechanics/optics.
