Question

If a base is added to water, what will occur?

Answer 1

This will increase the concentration of [OH-] ions.
For example:
- Ammonia NH3 (base):
NH3(aq) + H2O (l) → NH4+  + OH-

and 
-NaOH:
NaOH(s) + H2O(l) → Na+ + OH-
and KOH:
KOH(s) → K+(aq) + OH-(aq)

So we can see that the base increase the [OH-] & increase the characteristic anion [OH-] of the solvent.