I found this information but could not copy the internet address. The inventor said the following:
Ehsan – Special Guest
11/22/2010 3:29 PM
We do not recommend distilled water for any irons.The safest would be to use either bottled drinking water or filtered water which has taken the hard minerals out.
I tried again so here it the post, 7th one is his answer:
https://www.thegrommet.com/oliso-smart-steam-iron
I use tap water but put it thru a Brita water filter for my Rowenta.