I've found that coffee has no diuretic effect when the dose is lowered past that certain limit. I've also found that the body knows how to regulate a diuretic if it is dehydrated. It basically prevents the diuretic effect.
I don't think it's a good idea to get a diuretic effect if you're doing enemas or other flush-day activities like that because it could cause the body to try and absorb water through the colon. I would avoid that myself.
Matte tea doesn't seem to have the same diuretic effect but will certainly replace the need for coffee. It also has a ton of antioxidants and doesn't taste half bad (better than green tea.) It has a caffeine cousin named matteine which has a slightly different configuration than caffeine. It isn't acidic either.