Sorry, no it doesn't quite, NH.
1) 'tapwater with 8% green tea'-- 'tapwater', I think you mean, and with the % you don't really need 'concentration'.
2) '8%-concentration green tea water'-- I don't think you need the 'concentration' here either, but I guess it's OK.
3) '5-percent green tea drink'-- this is also clear this way. Now, I'm wondering if we should hyphenate 'green-tea' as an adjective...
Oh dear, I hope we get some more help on this one, NH.