I've been thinking about the long term problems of having to depend on nitrazorb to lower my nitrates - as my tap water is 60 Would it work to collect the rain water in a covered water butt (properly cleaned beforehand) then use that as a source for water changes? Hopefully far fewer nitrates?
My only worry is that bugs/parasites might colonize the water butt which could then be harmful to the fish. Does anyone have any thoughts on this subject?

It's not a good idea to use rain water for water changes. Rain water is basically the same as distilled water and does not contain the necessary minerals to make the water suitable for keeping fish. Plus, if you live in an industrialized area you don't have any idea of what kind of pollutants might get in the water.

A far better choice would be an inexpensive RO unit. In the US, you can get a 25 gallon per day RO unit for under $125.

Well, I'm glad you cleared that up for me. I've been hearing about RO on the plant forum and was wondering how it works, exactly. I'd sure appreciate the walk thru for dummies ...........

Hummm.... Now let me see.... Ummmmm. I think I'll let the people at Spectrapure do that walk through for you.

http://www.spectrapure.com/support_faq.htm

how is rainwater like RO water? it works for natural ponds etc. and wild fish..?

Unpolluted rain water contains nothing but plain old H2O just like distilled and RO/DI water.

The water in natural ponds, streams, lakes and rivers sit on or flow over rocks and dirt, where where the water dissolves the minerals that are necessary to keep fish healthy.

The type of rocks and dirt that are in an area determine the make up of the water in that area, and the type of fish and other wildlife will live there.
Such as: African lake Chiclids need very hard, high PH water to thrive or Discus from South America need very soft, low PH water to thrive.