Question

What role does water play in the litmus test

Answer 1

Without water, the acid or base will not dissociate into ions and give the colour change with litmus test.
Litmus is an acid/base indicator that indicates their presence in a solution by changing its colour. 
The colour change is possible only when acid or base dissociates into its constituent ions.
The dissociation into ions is only possible when acid or base is dissolved in water.
 

Answer 2

Answer:

with the help of water , acid and base react with each other and gives a suitable ions and colour . only water is used because it contains more intermolecular spaces between them