I suspect that rule isn't strictly observed but there are more wells than would-be dressers in the Malvern area so it all seems to work out.

I vaguely remember hearing that someone in ?north?east? central London had created a local well-dressing custom in a ?park?cityfarm? a few years back but I can't remember the details (tried googling but no luck).

P.S. Hope the "themes" tags are ok. I nicked the idea from forkedtongues.