Answer
Because of the relation between Polar covalent and Hydrogen, we know that there is a strong attraction force between Polar Covalent atoms and also a strong hydrogen attraction force between water molecules, thus if the polar covalent bonds did not exist, the hydrogen bonds would not be able to take place and the cohesion and thermal stability would be much less.
Work Step by Step
Pg. 49 The section on Thermal Stability and Cohesion. You can also refer back to the section on Polar Covalent and Hydrogen bonds to further explain the relation and answer, which i did. This is on Pg. 47
