Rainwater collection

[Apflanzeneh@webtv.net]

Hi all,
       I am planning a fishroom of approximately 600 gals. My current
method of water prep. would be unacceptable ( Tap water purifier, mixed
bed D.i) for small applications presently, 220gals. this is o.k .
Another alternative I know is r.o, but I think convincing my wife that
its for household use, and not for my fish (after using 60-100 gals a
week in my "room") just would'nt cut it! Plus my water is on a metering
system and I pay for every last drop . We are on a limestone aquifier, (
well water ) 
Tapwater : pH. 8.2 
k.h 5  Tetra test , 
gh. 9 Red sea test kit
      Does anyone have any expierences with rainwater collection, pros.
cons , different methods of collection? 
      Any input would be greatly appreciated!

Steve