Diluted sports drink
Small amounts of 1/2 sport drink & 1/2 water every 5-10 minutes (for example a teaspoon to tablespoon every time a commercial comes on tv) works well.
If the baby is having a wet diaper
every 2-3 hours you're getting enough in. Add formula
or breastmilk in small amounts. I like using the medication syringes you get from the pharmacy to measure.
Answer assisted by Mike Moore, Medical Student