I had this issue last summer when camping up at Virginia Highland Haven for a week -- for me it required the replacement of the shower cartridge. It was quick and easily handled for me. The only "issue" was I had to open the pipe access panel on the other side of the wall to hold the pipes "forward" when pushing the new cartridge in place as the pipes free float in the cavity space.
2011 Airstream International Serenity 28'
2016 Ford F250 Crew 4x4 KR Diesel