Question

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

Answer 1

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 

Answer 2

1.23x10^24 atoms/6.022x10^23 atom/mol = 2.04 mol H20