What is distilled water?
Distilled water is water that has been boiled into vapor and condensed back into liquid in a separate container. Impurities in the original water that do not boil below or near the boiling point of water remain in the original container. Thus, distilled water is one type of purified water.
Is distilled water a necessity with henna or Indigo?
Short answer: NO
Long answer: depends what your water is like; If tap water supply is hard water then better avoid using it . You can use mineral bottled water.
Using distilled water could be the best option but not necessity.