Unless your water is very hard, it will have little or no effect with most photo chemicals. Most developer, fixers, etc., contain sequestering agents, which lock up the mineral content, keeping it from affecting the active components. Toners are often very affected by water hardness; here it pays to use distilled water. Also, if you have high mineral content, it is a good idea to make your final wash a rinse in bottled or distilled water.(posted 8276 days ago)Don't try boiling water. That will actually make it harder, not softer, because you boil away the water, but not the minerals.
David Carper ILFORD Technical Service