Can one get sick from drinking too much home made Water Kefir?
Like most fermented beverages made at home, water kefir is safe to drink as long as you take proper sanitation precautions. If mold is growing, don't drink it, throw it out, and sanitize your vessels. Learn to look for signs of mold.

Fermented beverages like kefir and kombucha can become quite acidic and leech minerals from their container. Store them in glass.

I doubt there is any safety hazard from drinking too much if it is properly prepared. I suppose if it's acidic enough and you drink too much you could get a stomach ache.