>At least what used to be an issues, was DC currents plating out
>of materials, the LM1830 and other water sensing designs I have
>seen lately use AC currents to minimize the plating action.

This is part of the reason I saw for using a 10F200 series device at each 
sensor - the AC drive and detection, along with the communication.

I haven't looked at the National part, so don't know if it may also fulfill 
all the requirements. 

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