I'm having to put water tanks into a property that only has one rusty old fashioned galvo tank. Thought about slimline since the side entry to the house has the space but then thought....why would I want to look at any water tank? My yard is small and every meter counts. I do have an enormous deck though with nice flat and accessible space underneath that I don't use for storage and probably never will.

Anyone have experience with underdeck or bladder tanks? I'm in a high rainfall area 600mm average and it seems a waste to let the water run off into the storm water drain. Pro's, con's....?