I have a water stain (that looks like a water stain would appear on wood) in my fiberglass tub. It’s where the tub meets the wall on the opposite side of the shower head. There is a water supply line to the toilet near this. What could this mean? (And, is this something I can fix myself?)picture of water stain damage in fiberglass tub

  • What have you tried to remove that discoloration? Is anything evident on the other side of the wall from the shower? How about the floor, where the shower pan meets? If no other evidence, I'm thinking this is just a discoloration and not evidence of a leak.
    – RMDman
    Commented Aug 11, 2023 at 14:44
  • I tried baking soda and vinegar with no success. Nothing on the floor (and actually I’ve torn up the floor, the subfloor is clean in that area) and there’s nothing on the other side — I guess it’s just a stain but it’s in such a weird place it looks suspicious. Thanks!
    – Lisa
    Commented Aug 11, 2023 at 15:23
  • Kinda looks like the paint leached onto the tub...same green color, no?
    – Huesmann
    Commented Aug 12, 2023 at 12:46
  • @Huesmann - can't be that, it's a brand new paint color. I had a plumber come look at it, and he confirmed it's just a water stain and really nothing to worry about. Thanks!
    – Lisa
    Commented Feb 5 at 20:30

1 Answer 1


Why not use a stain remover intended for iron stains, which are often brownish, such as Red-B-Gone or Iron OUT? These may contain EDTA, sodium hydrosulfite and other chemicals that actually remove rust stains, which that appears to be. One of those cleaners would be worth testing, but...

If the stain is within the fibers of the fiberglass tub, as might have occurred if some substance entered at the outside edge and was wicked into the material by capillary attraction, the only feasible remedy would be to cover the stain, and the rest of the tub, with a water-proof fiberglass-compatible paint.

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