Well... i dont know if a shower affects your high... but certainly taking a shower while stoned is a trippy thing... i could feel every drop of water, separatedly... the worst part was that some drops were colder, and some drops were hotter, so the overall effect was very confusing... also the water felt much more "oily", "viscous"... and always there is the danger of falling and hurting yourself... so... you may try it, but be sure of what youre doing.

PS. What i said is valid only for hot/warm shower. Cold shower (or cold weather, or just to feel cold) actually kills the high.