Question

how can you explain that the three states of water are interchangable

Answer 1

ice can be melted to water
water can be evaporated to gas
gas can be condensed to water
water can be freezed to ice.

Answer 2

Hey Friend !

The three states of Water are interchangeable. 

The 3 states of water are: solid(ice) , Liquid(water in room temp.) and Gas (water vapour).
______________________________________________________________

when you heat water which is in room temperature it will change into water vapour, i.e, Gas . the change taking place is Liquid ⇒ Gas.

______________________________________________________________

When the water vapour touches a surface , it condenses and changes back into liquid, i.e, Water.
the change taking place is Gas → Liquid .
______________________________________________________________

When you keep normal water in a freezer, it becomes Ice, i.e, Solid.

The change taking place is Liquid → Solid.

______________________________________________________________

When you keep an ice cube outside in room temperature, it gradually melts and changes into normal water.
The change taking place is Solid → Liquid

===========================================================
Hence the 3 states of water are interchangeable :)

HOPE IT HELPS :)