Re: My Father's tap/spring water turns blue when soap is added, why?

What a neat problem!  
As a rule, blue color in a water supply is caused by relatively high 
levels of copper II ions.  
Another factor in water that might cause a color change is an alteration 
in pH.  
In order to test this, I dissolved a small granule of copper sulfate in 
about 50 ml of reagent grade water.  Adding a little dilute hydrochloric 
acid didn't change the amount of color, but adding a few pellets of sodium 
hydroxide caused an increase in the intensity of blue color.  
You didn't specify what kind of soap your father was using, but 
traditionally soap is made by base hydrolysis of animal fats into fatty 
acids.  In order to drive the hydrolysis to completion, excess base is 
added and it is consequently found that the final product is quite basic.  
I'm going to hypothesize that 
1.  your spring water is mildly corrosive and is dissolving copper from 
somewhere, perhaps a copper pipe, but the amount of copper dissolved in 
the water isn't high enough to notice.
2.  You're using a high pH soap, which might intensify the color to the 
point that you can notice it. 

  
2.