Instruct: Classify a given Amazon review into positive or negative sentiment.
Query: Great until it stopped working

I've had two of these units now, and both of them quit after about 4 months for no reason I can figure out. You should use distilled water, or you'll find yourself taking the thing apart and cleaning the mineral build-up off every couple of weeks or so. While it was working though, it was pretty good. I'd recommend a humidifier with manual controls instead of digital, as that was what first stopped working.