Answer: Hydrogen Bonding
Explanation: Hydrogen Bonding is that kind of forces of attraction which can only be present in the molecules having electronegative atom and the hydrogen atom attached to it.
Thus water molecules have both Oxygen atom as the electronegative atom and hydrogen attached to electronegative atom O.
Thus one H atom of one water molecule forms hydrogen bond with oxygen atom of another molecule .
And these hydrogen bonds are weaker than the normal covalent bonds.