IPhone 3GS exposed to water still works - but for how long?

My iPhone 3GS was submerged in clean water for no more than two seconds about a week ago. It never turned off and kept working perfectly. A week later, the only sign of the unfortunate event is that the water-damage indicator in the headphone jack has been tripped to the half-pink, half-white state. I know I'm really lucky that it's worked out this way so far, but how long is this going to last? Should I expect the phone to s*** the bed in a couple weeks or months? Thanks.