# How do you know if it's not a Water Molecule?

Because water is SPECIFIED to be ${H}_{2} O$, i.e. oxygen in the $O \left(- I I\right)$ state......
If you have $H - O - O - H$, we gots oxygen in the $\stackrel{- I}{O}$ state....the $O - O$ bond is relatively weak, and its length is $1.474 \times {10}^{-} 10 \cdot m$.