Unfortunately, I haven't seen a good one. I believe there are more people interested in milk grains than water grains therefore less attention was given in this area. I have been trying to make water kefir for months but struggled to the point where I am about to give up.
I belong to different kefir forums where most people talk about their milk grains with a handful of them still interested in growing water grains. I personally believe people use milk grains more often simply because they are less fussy (at least mine are like that) and that water kefir tends to have a higher alcohol content thus less kids friendly. So making milk kefir you won't have to worry about turning your little ones into alcoholics! LOLOL
There are two Yahoo groups currently very active with lots of information available. Both milk and water kefir are discussed in both forums. I have to warn you though, while some of these forum members are friendly and helpful a large number of them are very opinionated and sometimes, down right rude. When I first started making milk kefir I used 1% or skim milk. The first time I posted there, some forum people were so mad at me that I thought they were going to burn me at the stake and sacrifice me to their kefir gods. I never went back. I did receive some advice on water grains but every bit of information I received was confusing and contradicting each other.
Currently, I am resting my water grains in sugar water in the fridge. If you find anything that is useful please let me know.