leak detecting tape?

[NeverDie]

The sensor circuit itself doesn't look complicated:

Here you can see where I soldered a 2.2MegaOhm resistor in-line with the speaker.  It's driven by a AC circuit, so, interestingly, I found that even if I completely severed the red wire, the alarm was still audible.  Anyhow, 2.2MegaOhm keeps the alarm muted but still loud enough to hear.

 

[NeverDie]

The detection mat actually fits pretty nicely on the floor of the cabinet:

I ended up not trimming it at all.  
 
 

 

[NeverDie]

Here's the first "dry fit" with the protective mat on top of the detecting mat and then the RO tank and a couple other objects on top of the protective mat:

I'm sure we'll cut the protective mat to fit, and my wife will undoubtedly fine-tune the final layout of things, but it gives you an idea of what installed product might look like.  
 
Looking under the kitchen sink like this tends to remind me of various scenes from the Terry Gilliam movie Brazil.   B) 
 
Thanks again to RAL for suggesting the One Drop Mat.     
 
"We're all in it together!"