I have an Indian Bean tree which is slow growing in my patch a friend has one also but they can get large so it's always a good policy to plant any tree a sensible distance from building foundations. Rule of thumb is the root size is equal to the top growth of an average tree ( imagine turning a tree upside down & this gives you the root size ). Have to say my Catalpa is 'Aurea' so it will be slower in growth than the usual green type due to less chlorophyll. As to water it will require the usual amount of any tree. They are beautiful trees but I thought I'd lost mine this particularly harsh winter this year but it did eventually show signs of growth. ' Whew ' !!!

Just to add...not sure about this particular tree, but root growth can far exceed the crown size of many trees.....How about cutting this tree back hard every year and keeping it as a shrub, that way you get bigger better leaves, plus the root growth will certainly be less of an issue.