@Dean-And-Stacey0 I'll add my vote to no refund. We need to train guests to be adaptable to situations outside the host's control, not think that they'll have money throw at them for any small inconvenience. A refund doesn't help the father and kids to have had a shower last night.
If the water was off for an entire day, that might be different, but overnight, when they were asleep for most of that time, isn't some huge impact.
As far as phone calls- I wouldn't shut my phone off, in case there really is an emergency situation, but I would make it clear to guests that you are available by phone for non-emergencies from XX hr- YY hr. and make a short list of what constitutes an emergency- it's not that they can't find the spatula.
(just in case you think that's an absurdity that would never happen, there was a post here from a home-share host whose guest knocked on her bedroom door at 2AM to say that she couldn't find the hair dryer)