The aqueducts increase the "amount" a water carrier carries.
It adds 1 to that number, so if it says you have 1 water ps, but have 10 aqueducts, you should get 10 water per second.
but the numbers in this game are strange (although it might just be that my pc can't keep up, since it's a bad one.) so it's not entirely true that it's a XxY formula.