Does whey protein build good muscle or is it water wight?

Whey protein is a good source of protein, it has all the essential amino acid (the ones your body can't produce), amino acids its what repairs muscle tissue, in order to build muscle you need to do hypertrophy excercises and take 1~2 grams of protein per pound of lean body mass.

Whey protein by itself will not build muscle, but is a good kind of protein like eggs or chicken, the difference is that Whey has a faster absorbtion.