Quote Originally Posted by Ian Grant View Post
At one time manufacturers recommended boiling water and letting it cool and settle, fitering if needed, this would remove the worst of the hardness from the water and make a significant differance.
Yes, the are two types of hardness; temporary hardness and permanent hardness. The temporary hardness is from calcium bicarbonate formed from water containing dissolved carbon dioxide flowing over limestone.

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.