Recently got a gallon of distilled water at the local supermarket, no problem with supply. I use it to mix TF-5 on Photoformulary's recommendation. Not sure it's necessary. Many years ago I heard Oliver Gagliani enthuse about the quality of water he got in South San Francisco, from Hetch Hetchy reservoir. Our water comes from a similar watershed, the Mokelumne River so I figure I'm good; experience has borne this out.
David