“It was just another riff, like Into The Fire. We didn’t make a big deal out of it and it wasn’t being considered as a track for the album": Ian Gillan on the unlikely success story of writing and recording Deep Purple's Smoke On The Water
'The downdraft from the mountains caused the smoke to blow across Lake Geneva, like a film set or dry ice on a stage show. At this point, Roger wrote the words ‘smoke on the water’ on a napkin”
https://www.musicradar.com/news/deep-purple-smoke-on-the-water-interview-iangillan-ritchie-blackmore