I really have no idea of what your experience level is, nor do I care. I only hope my post will allow you to think.
Water monitors commonly(they should easily under normal care) reach 6 foot for females and over 7 for males.
With that in mind, how does an 8 foot cage meet even the most minor of a water monitors needs? I am thinking the pond to be a WATER MONITOR, should be that size.
So all in all, it appears your monitors are not all that needy(quote from my wife)
If I were you, I would rethink what a monitor is, because an 8ft cage barely meets the needs of an ackie(two foot lizard)
To clear it up a little, I personally would rather live 3 or 4 years in a large cage(cell) then 15 years in a tiny cage(cell) To me, keeping a animal confined in a tiny cage for long periods is not something to brag about, but more about how well it was tortured. Please consider, thats only my personal thoughts, which is what these forums are for.
I appear to be the only one brave enough to make you mad, but thats not my intention. I just would love you to think about a large monitor stuffed in a small cage. Cheers