What is the cleansing power of water?

You should be made aware of the cleansing property of water. 

I refer to this in an outdoor sense. 

A stream of running water is death to all smaller evil personalities. 

You will recall the legend of the witches who could not cross any stream of running water. 

There was a great psychic truth in that notion. 

Stagnant water harbours evil spirits, but clear and moving streams purify all in their vicinity and safeguards.

Letters from Harry and Helen