Really they like ericaceous soil/compost and should only have rain water if you are in an area with hard water.

Mine are flourishing in a neutral clayish soil (not ericaceous by any stretch of the imagination) in front of a low south facing bank, which is surprising as to stay blue they normally want an acid soil. They like plenty of moisture.
If you find your blue one tends to go pink you can buy a special compound to blue them up again, so go for it, as long as your ground is not too dry.