# Changes in Water Bonding Angle

I heard something recently in a casual discussion, but have yet to be able to confirm it: is there any evidence that the bonding angle for a water molecule, currently defined as 104.5, has been either steadily growing or shrinking since it was first observed and measured? Is there any possibility that water samples from different locales would produce different results? I am speaking strictly of water in as pure a form as possible, not water affected by impurities or physical manipulation.

It should also be noted that the bond angle can both be calculated from theory and measured from experiment, and neither method yields exactly $104.5^\circ$. Now your theoretical calculations might improve if you make fewer simplifying assumptions than your predecessors, and your measurements might improve if you develop better apparatus and technique, but the true underlying value of the bond angle is not changing.
1 Defined here as oxygen-16 bonded to two atoms of hydrogen-1. Now the angle could vary with isotopic abundances, so perhaps someone was referring to changing isotopic abundances of a source of water. You might see this, for instance, in extreme climate change, since as temperatures rise the fraction of "heavy" water ($\mathrm{D}_2\mathrm{O}$, etc.) evaporated from oceans increases relative to "normal" water.