Although the above are reflux stills in most cases, intended for alcohol, there are many others for water: http://www.jenconsusa.com/10-Water-S...ill-4000X.html and if you look at the dimensions you will see how small these are.
I am not advocating any method, just stating the fact that you can use either, and that there are advantages and disadvantages to both methods (distillation or deionization).
The bottom line is that all commercial developers and fixers are designed to work with tap water. They contain ingredients that prevent particulate matter from forming from hard water. And so, a true test is to mix some developer with tap water and look for the formation of sediment. I know that that is a harsh way to test due to expense if the test fails, but then it does work.
I don't use DW myself for mixing anything but materials for emulsion making. At EK, I did the same. We had tap water to use to test formulas with. And, what I have said goes for both color and B&W.
I thank everyone for their input, but I think I have my answers and this thread has run it's course.
H2O + CO2 + CaCO3 ---> Ca(HCO3)2
Boiling the water reverses the above reaction and the resultant calcium carbonate which is insoluble will settle out. The permanent hardness is from various magnesium salts such as magnesium chloride in the water and they are unaffected by boiling. However, the permanent hardness is usually not a problem for photographers.
Bring the water to a full rolling boil for 5 to 10 minutes in an uncovered container of glass, stainless steel, or agate ware. Cover and allow it to cool overnight. Decant or filter off the softened water.
i'd use britta-filtered water to eliminate calciumdeposits and 0.5g/l of edta(photo calgon)if that is not good enough.works wonders to make good tea too. the latter being an opportunity to share the expense.