Sorry for posting this again, I don't know if the question was skipped or not, but I was just wondering if I could get some help on this... thanks.

Question

There are 3 known isotopes of Hydrogen and 3 stable isotopes of oxygen. How many types of water molecules would these produce?

Order wouldn't matter then.. right? So then it would be a combination instead of permutation?

This problem is one for statistics. Permutations and combinations.
But look at it this way. It won't get the answer but there are a LOT of different combinations. I don't know the formula but someone surely will post it for you.
H H H O O O H H H
1 2 3 1 2 3 1 2 3

Since there are two H atoms, we can have something like this,
1,1,1 which means H¹O¹⁶H¹

1,1,2
1,1,3
1,2,1
1,2,2
1,2,3
1,3,1
1,3,2
1,3,3
etc. You get the idea.

H²O¹⁶H¹ is the same as H¹O¹⁶H² because the H atoms are equivalent.