Tap water that's safe for human consumption will be safe for your snake.

I've personally never re-frozen a feeder after refusal, but have seen enough threads to believe its ok. Plus, in tttaylorrr I trust, so I will give my endorsement as well. After that, until you have multiple snakes, tossing it is just part of snake keeping. Either toss it in the trash or if you live somewhere fairly rural, just toss it outside, something will eat it. That's what I do when I catch one in a trap. I just toss it outside and it's always gone by morning.