Write the equation for the dissociation and re-formation of water.?

Answer 1

dissociation of water is the formation of ions from water to give H+ and OH- ions as follows:

H2O (l) <--> H+(aq) + OH- (aq)

note that the double arrow refers to dissociation, also meaning that the reaction can go either way, thus re-forming water.

FYI, the following is the electrophoresis of water
H2O(l) --> H2 (g) + 1/2 O2 (g)
this is irreversible. at least on earth. to reverse this equation, it would be the combustion of hydrogen gas to give water:
H2(g) + 1/2 O2(g) --> H2O (l)

hope this helps! :)

Answer 2

Wikipedia
electrolysis
go

Answer 3

2 H2O <--> 2 H2 + O2