Hello Mr. Rawles:
I expect you have already heard about this problem, but the black Berkey water filters have an alarmingly high failure rate (in my personal experience, for what it's worth, 4 out of 4). The silicone caulk that attaches the black ceramic-like filter itself to it's plastic base fails, and water runs right through the failure spot, without being passed through the filter material. People could be unknowingly drinking unfiltered water, as I was. I read online that adding red food coloring is one way to test the integrity of the filter unit, I do not know if this is true. Thank you, as always, for everything you do, I have received so very much from you. - Carol D.
JWR Replies: Sending them back to the company under warranty for a free replacement works. (At least it does now--a couple of years ago, they just mailed you back identical filters that also failed.) But I learned that there is also a practical way to fix them yourself.