polar covalent bond

Please take a look at the image of polar covalent bond in the $\ce{H2O}$ molecule below. My question is given in **bold type** in the following discussion.
![polar covalent bonds in H2O](https://i.stack.imgur.com/K3V3B.jpg)


Here is my flow of thought that confused me so much :


1. $\ce{H}$ atom is slightly positive and $\ce{O}$ atom is slightly negative.
2. Positive and negative charges attract one another, no matter how small their charge is.
3. Ionic bonds happen between atoms that have different charges. for example, $\ce{NaCl}$. $\ce{Na}$ atoms have positive charges and $\ce{Cl}$ atoms have negative charges.
4. So, in the image above, hydrogen and oxygen in $\ce{H2O}$ should behave just like $\ce{NaCl}$. What I mean by "behave" is that they should form ionic bonds just like $\ce{NaCl}$. $\ce{H}$ and $\ce{O}$ have different charges. $\ce{Na}$ and $\ce{Cl}$ also have different charges. **Based on this argument, why does $\ce{NaCl}$ form ionic bonds but $\ce{H2O}$ does not?**


I understand the basic difference between covalent and ionic bonds & polar and nonpolar covalent bonds. But based on my line of reasoning above, what prevent molecules with polar covalent bonds from turning into ionic bonds? They have different charges, just like molecules in ionic bonds?


Do I have some basic misconception about polar covalent bonds and ionic bonds? Thank you for answering. I really appreciate it, this question has been bugging me for a while.


