Home Distiller

I’ve been reading quite a bit through here, and in a lot of the recipes they just say so many gallons of water. But in documentation that has come with the one kit of ingredients, I ordered to get my feet wet, they said I needed to use distilled water. Is that important? I used distilled water, and if that is what is required I absolutely will continue to do so. I’m just curious if that is just an assumed piece of knowledge, so when individuals are saying 4 gallons of water, they mean distilled water and there is an understanding. Just trying to learn. Thanks in advance.