Would de-ionized water ruin a fuel cell?
DI water only removes dissolved salts (the majority if impurities in water). It does not remove dissolved/suspended organic compounds, gasses, etc. For a hobby kit, I doubt it will make much difference- I expect that the electrolysis part of your experiment might have buildups after a while, but the minute amounts aren’t going to affect you too badly. your mileage may vary, however.
