That’s the thing, you put the new roll at top and it collects in a spool on the bottom. Provided the new cylinder is sterile, you’re all good. The problem arise when it reaches the end of the spool and isn’t changed do people are using the same static towel, or people cheap out by trying to reuse the dirty ones
Canals can be useful for this as well, Lowell MA used to have a huge industry all on waterfronts