In a previous thread, on Fx50, I mentioned that I used bottled water to mix my solutions. In one of the responses it was asked why I didn't use distilled water. The answer to this is that it is simply not available (as far as I can tell) in the UK. De-ionized water is invariably offered as an alternative. However, on page 190 of The Negative (A.Adams esq.) he counsels against the use of "softened" water saying that the removal of Calcium (as well as its exchange for other ions) is not ideal for photographic developers: "after softening, [the water] may have only 20ppm [of Ca++]. I understand that 180 to 200 ppm of calcium is ideal for most photographic processes." So, my questions are a. am I correct in thinking that de-ionized water has its calcium exchanged for sodium? b. is AA correct that it's needed? c. where can I get truly "distilled" water in the UK?