Question

How does hydrogen bonding in water affects Density?

Answer 1

Basically it increases the molar mass; i.e., if you have H2O vapor the molar mass is 18 but if you have a dimer (H2O)2 or trimer (H2O)3 the molar mass would be 36 or 54. In practice you get some kind of an average because these link ups are quasi-stable.