A.F.
From the Texas Children's Pediactric Associate's patient resources:
Offer clear fluids (not milk) in small amounts until 8 hours have passed without vomiting.
For a child over 1 year old with vomiting (but no diarrhea), the best fluid is water or ice chips because water can be directly absorbed across the stomach wall. If your child is 2 years old or older water is best, but half-strength lemon-lime soda or Popsicles are also okay. Stir the soda until no fizz remains (the bubbles inflate the stomach and increase the chances of continued vomiting).
Start with 1 teaspoon to 1 tablespoon of the clear fluid, depending on your child's age, every 5 minutes. After 4 hours without vomiting, double the amount each hour. If your child vomits using this treatment, rest the stomach completely for 1 hour and then start over but with smaller amounts. This one-swallow-at-a-time spoonfed approach rarely fails.
A nurse line told me that you only get concerned with dehydration when he doesn't urinate for 12 hours or more.