How many moles of water are in 1.23 x 10^18 water molecules?

Divide the number of molecules you have by, 6.022 x 10^23. This will give you the mols of water, or the mols of anything, since there is always 6.022 x 10^23 molecules in 1 mol of substance. 
1.23x10^24 atoms/6.022x10^23 atom/mol = 2.04 mol H20 

Atomicity occurs to prevent updates of the database occurring only partially, which can cause greater problems than rejecting the whole series outright.some are monatomic, diatomic, triatomic etc because it shows the number of atoms. for example, monatomic means it contains only one atom.

The mass has escaped into a gas which you can not see so the law stays true.