My lovely GP has given me some great advise about staying hydrated during norovirus and I thought I'd share it.
Take a teaspoon of water every two minutes. This isn't enough for your body to reject (ie vomit) and should be absorbed almost instantly.
When you feel like you can cope with this, take 2 teaspoons every 4 mins....and so on until you can stomach dyrolite, lucazade, flat coke.
If you start vomiting again go back to the teaspoon of water every 2 mins.