The only thing I can sort of think of about that is that I can see the reservoir getting pumped empty in a manner of minutes whereas we usually need to run a sprinkler for 20 minutes in an area to get your 1cm. I dunno, I just sorta envisioning this being an expensive proposition for you (a high flow high pressure pump must exist but I see it being pricey), but then again I could be way off base.
I think you don't have to be a hippie to appreciate those low volume dripper style irrigation systems, and you could feed that with a rain barrell filled with RO wastewater.
Then again I guess I'm just trying to influence you into doing what I was sort of one day hoping to do myself, so if you do come up with a different idea that's cool too.
Good luck with whatever you come up with, I'm sure there are some good ideas to be be found.
