The tensioner bolts onto the pump.
It appears to be "conventional wisdom" to replace the water pump, the timing belt and the tensioner at the same time - and you'll often see advice to this effect, accompanied by such gems of wisdom, as you might as well do it whilst you're in there.
Personally - I've never understood why - given the fact that it's my time (to replace the parts) & my money (to purchase the parts), I would rather consider the pump as one entity, and the belt & tensioner, as another - and replace the one that is bad - I don't exactly see the point in replacing functional parts.
The last time I changed a belt, I didn't bother to touch the pump, and a year and a half later, it was still going strong. I did replace the pump at that point, along with the belt & tensioner - but that was done as a part of a "full rebuild" - and all of them could have been reused, had I so chosen.
Just my $0.02