I'm not entirely sure I understand the situation you want to create but I'll take a shot.

If you use seperate water sources for each enclosure and only share the overflow reservoir it should be fine.

If you want to use the overflow and pump the reclaimed water back into both enclosures then I would recommend against it.

The short list of why goes like this: Parasites, disease, toxins, etc.

I would keep them completely seperate.