Can it kill my baby if I give him 2% milky mixed with a little water

It's not good for him at this age. Generally milk isn't given until the baby is at least 10 months of age, and at that age whole milk (milk that's high in fat and protein) is given, not watered down 2%, and it's not given all the time.

The best thing for your baby at this age is breast milk or formula.