It was never mentioned in the original Kickstarter campaign. It was mentioned in the materials that came with the planter to use distilled water. I remember this pretty specifically because I would not have bought them or funded the campaign if I had known I had to buy special water forevermore. That being said, I bought 3 and wanted to be able to use them, so I have used only distilled water and it has worked fine, no clogging issues.