Rainwater Collection / Pond Water Storage (Tower) Support Question
This is a stunningly bad idea, IMHO. As @Comintern notes, that's a rather significant load to plop beside your house.  Far simpler and safer to run your downspouts over to where your sump pump discharges, and put a basin &amp; pump there that pumps water uphill, to your storage tanks, set somewhere uphill, so they will provide water pressure when you are without power, if that's your concern. You could even put a hand pump in the system alongside the electrical one if you like. Or you could construct a much less scary (far less weight) structure that carried a trough or pipe from your gutters to the storage tank. If you lack a suitable hill, you could build one at a safe distance from the house and convenient to the garden with a few dump-truck-loads of rock/gravel...

You would definitely need a reinforced slab to spread the load, and calling an engineer would be the right choice if you proceed down that path. What is your seismic hazard level? I'm in a "very low risk area" and I would still be quite concerned to have the structure you describe next to my house in the infrequent, rather minor and mostly far away quakes we have.