I am really keen to get a clear picture on this because a friend just had his Tag fail in the Jacuzzi.
This link might be useful http://www.wristwatchreview.com/2010/04/15/omg-dont-wear-your-watches-in-the-shower/ our advice is never to use any watch in a shower bath or Jacuzzi because the watch can leak due to the high temperature of the water and / or steam. The other issue is that shower gel and bath foam can destroy the seals causing the watch to leak. In fairness I have worn watches in the shower without any problems but when the heat of the water is combined with the issue of detergents mentioned above which combine to cause both expansion of the metal case and degradation of the seals there is definate potential for problems in the future and it's very risky. Of course in my case working for a watch repair centre it would not be quite so catastrophic but it would still cost me money to sort out and be annoying. Although as I say I don't always follow this rule myself I still say to clients "why take the risk of getting water into the watch and having the inconvenience to get the watch repaired when you can just take the watch off?" there is one other factor that comes into play though which is that many watches are damaged by being dropped on a tiled floor in bathrooms so that needs to be considered too because watches being dropped is one of the main causes of them needing repair.