I gave my dogs bottled water once, because I thought our water tasted funny and they refused to drink tap again.  It was getting ridiculous buying bottled water for two large dogs, so I splurged and got this.  Best splurge EVER! My dogs drank it, before I checked it, so I knew it was good. I just checked it and had to keep going back and force because I could not believe it.  0.78 and it says when the filter water was passed 0.06 to worry. The filter water still reads 0.00 and my tap water around .7-.8 after a couple of months.  This is filling it up multiple times a day for my two large dogs and family. So the filter lasts with bad water.  It is actually doing better than my true hepa air filter in my air purifier.   I think it will last longer than my air filter and that is expensive! If you have bad water and pets, I highly recommend getting this. MUST HAVE.