And since water is the only molecule present in our mixture, that means water must associate. And let's see exactly what happens. Remember, water can act as both a base and an acid. So what actually happens is two water molecules interact in such a way that one acts as a base and one act as an acid. So one donates H, and the other one accepts H, forming a conjugate acid and a conjugate base, namely hydronium and hydroxide. And this process of dissociation is called autoionization, where the auto basically means that two water molecules interact.