Is your water still ice-cold?
If not, you can take your cock out briefly while you get fresh water... but don't think that means you can get an erection!
From now on, every time the water starts to get warm, you have to change it before you continue. If you have ice-cubes in the glass that shouldn't be too much of a problem though...
I'm going to get the shower-head and rinse all this soap off!
You can have another 30 seconds in the cold water.
And as always, you know the rule if you start to get aroused...