Not yet, but I'm very seriously considering it. I've just moved house and the water pressure here is very low. My RO unit production has gone right down,
My house is the end of a terrace of three and there is only one down pipe - in my garden - so I get a huge amount of rainwater from the roofs of three houses.
I've tested rainwater and had readings between 002 and 006. The 002 was caught directly from the sky. The 006 was from the roof. Of course, these readings come from a standard tds meter, so may be inaccurate.
As far as I can see, all that is needed is a diverter fitted in the downspout which directs water into the water storage butt or IBC. Maybe fitting a strainer would be a good idea.
I don't know about putting the water through a DI unit to bring the tds reading down to 000.
Dare I suggest that this is an excellent DIY project?