Tunze osmosulator. I've had one in my 90 for 6 years now....flawlessly doing it's job.
Only issue is the pump can't be too far away. Mine is in the basement so it can pump up about 8 feet of headpressure.
If you have to go a long distance from your supply, you will need a peristaltic pump. In that case, other than cost, the litermeter III is awesome. I've tried other methods on my nano with JBJ but finding a suitable pump (moving water around 35 feet) was a problem. The pump I have is noisy and big.
All in all, the osmosulator has all the safety features and reliability and I'm very comfortable recommending it.